* { color: black; }

Or to just make your post text black,

.postarea { color: black; }

Or, you can use the Colors tool in the Customizer (https://ncforaj.wordpress.com/wp-admin/customize.php#colors) to set black as your text color. The text circle is the one on the bottom right.

How do I change the color on the post comment section that asks the visitor to comment?

Do you mean the text on single posts that says, "Leave a Reply"?

To change the "Leave a Reply" text color on single posts in the Pachyderm theme, add this to your Appearance → Themes → Customize → CSS panel:

#respond h3 {
	color: #99b2b7;
}

Adjust the color code as needed.

How do I make the post bigger when someone clicks on it?

Do you mean make the main content area wider?

Here is an example that will expand the main content area by 100 pixels. Note that this will affect all types of content, not just single posts:

#main {
	width: 700px;
}

.active-sidebar-primary-sidebar #page,
.page-template-nosidebar-page-php #page {
	width: 890px;
}

How I change the color of the page tabs on Pachyderm?

The first thing I would recommend would be to change the entire color palette using the custom colors feature at Appearance → Themes → Customize → Colors panel.

If you'd like to get more fine-grained control, you can write some custom CSS to make color changes.

Here is an example showing how to change the menu navigation colors for the Pachyderm theme:

.navigation-main {
	background-color: #99b2b7;
}
.navigation-main a {
	background-color: #99b2b7;
}
.navigation-main li:hover > a,
.navigation-main ul ul :hover > a {
	background-color: #adc1c5;
}
.navigation-main li.current_page_item ul a,
.navigation-main li.current-menu-item ul a {
	background-color: #99b2b7;
}
.menu-toggle {
	background-color: #99b2b7;
}

Also, I wanted to know how I could change the hover color of the tabs under the header/title. Its still the original pink.

The ".navigation-main li:hover > a" part of the example code above covers that.

Today I looked at my blog and all of a sudden, the main table background color has turned grey. It has always been white ever since I started it and I'm not sure what has happened nor can I figure out what to do. I've been trying to insert code in a dozen of places in CSS code, but nothing works. Can someone help please?

I have changed my imbalance 2 footer by using CSS and it all worked fine. I've been using it for a while now. However: All of a sudden, my footer area is showing in grey instead of white although the color is defined to be white...

I have been using an image as site background and switched to a plain color lately and I am pretty sure the problem didn't occur until the switch. Does anyone know how to solve that?

I'd be very grateful for your help!

Cheers,
Anna

http://anemina.com

The Grisaille theme only supports three colors in the Custom Colors section: background color, links hover color, and links color. However, you can use custom CSS to set colors for other elements on the page. If you aren't familiar with CSS, you may want to start by looking at these links:

Editing CSS CSS Basics

If you have any questions about this, please let me know!

The other major piece of the puzzle I was missing was figuring out that a:hover can only come after a and a:visited have been set. That was making some things behave strangely.

Thanks to you I've got everything sorted :)

Now I just need to save all these customizations in a text file somewhere before I lose them in an update or something.

.comments-area .bypostauthor cite span {
    background-color: rgba(230, 230, 230, 0.1);
    background-image: -moz-linear-gradient(center top , rgba(244, 244, 244, 0.8), rgba(230, 230, 230, 0.8));
    background-repeat: repeat-x;
    border: 1px solid #1F6F93;
    border-radius: 2px 2px 2px 2px;
    box-shadow: none;
    color: #1A5F7E;
    font-size: 0.714286rem;
    font-weight: normal;
    line-height: 1.42857;
    margin-left: 0.357143rem;
    padding: 0.142857rem 0.357143rem;
}

And careful with stylesheets you find elsewhere. The one you found is ok, but often it might not be the wordpress.COM version of the theme. Better use WP's own:
https://wpcom-themes.svn.automattic.com/
https://wpcom-themes.svn.automattic.com/twentytwelve/style.css

The only one I'm still being tripped up by is .bypostauthor, as there doesn't seem to be a ".bypostauthor cite span a" in the CSS, only three instances of ".bypostauthor cite span" and a couple ".bypostauthor cite b".

None of them, as far as I've been able to discern, are capable of changing the color of the "post author" text on the tab next to comments. At least, not with a "color:" command.

Now, consulting the original stylesheet of the theme will be useful, but the best thing to do is learn to use a developer extension, so you can examine the actual pages of your blog, see the selector for each element and the rules that are applied to it, and even try out changes. I don't use Chrome so I'm not sure about it: I think it includes Development Tools. If it doesn't, you can add it. Or you can add Firebug lite.

Now, your questions:

.comment-content a
= links in the main text of comments

a.comment-reply-link
= the "Reply" link that shows below a comment if you have enabled nested comments

.comments-link a
= the link that shows on the main posts page ("Leave a reply", "1 Reply", "2 Replies" etc)

(If you're wondering why "a" after or "a" before: ".whatever" specifies a class of similar elements; so "a.whatever" means any link that's specified as whatever, but ".whatever a" means unspecified links inside any section that's specified as whatever. Clear or confusing?)

.comment-link
doesn't exist in the CSS of 2012

.bypostauthor cite span a
= a tab next to the comment author's name; marks that this commenter is the author of the post.
I think it's visible to visitors only. Check the theme demo:
http://twentytwelvedemo.wordpress.com/2011/07/07/fall-in-luxembourg/

"the selector that changes the link color on comment author's names":
.comments-area article header cite a

(Since you like clearing things up, let the pedant in me note that your phrase isn't really correct. As you certainly understand, what changes things is the rules inside the brackets, not the selector!)

Before going into this I only knew a bare minimum of CSS from HTML coding years ago, so I thought I was going to get away with just a, a:visited, and a:hover. When that didn't work I spent some time Googling trying to figure out how to customize WordPress and I kinda cannibalized the other terms such as .entry-content from reading other people's posts and just experimented with them until I found ones that fit. So it's entirely possible there are some useless ones in there (for instance I am using both .widget and .widget-area without any real understanding of which does what, just that it looks like what I need it to now). When I couldn't get any further on my own I came here.

Theme is Twenty Twelve and I've been looking around a bit for a readymade list of every selector in it because that seems like something that should be available, but no luck so far.

If you can stomach me for a couple more questions, I was wondering which selector is controlling the color of links left in comments? Is it .comment-content or .comment-link? What is the difference between the two, anyway? It seems like the former should control links in comments and the latter is redundant with a.comment-reply-link?

Additionally, you had mentioned .bypostauthor cite span to "change the tab next to the comment author link" but I see no such tab? I tried using that line to change the color in which the comment author's names show up, but it didn't seem to have any effect when used like:

.bypostauthor cite span a, .bypostauthor cite span a:visited, etc.

If this isn't the selector that changes the link color on comment author's names, do you know which is?

As I said/showed, you use the exact same selector plus the addition, no matter what the selector looks like (no matter if it's one word or more, no matter if it has punctuation marks and spaces or not, no matter if it looks like others or not). What you have confused is that the addition for, say, the hover isn't a:hover, it's just :hover. If the selector for an element is
#what-the-f-is .this
the selector for the same element on mouseover is
#what-the-f-is .this:hover
Therefore:
a.comment-reply-link
a.comment-reply-link:visited
a.comment-reply-link:hover

#wrapper {
    background-color: #456789;
}

Replace 456789 with the hex for the color you prefer. If you're not familiar with hex color numbers, see here:
http://www.december.com/html/spec/color.html

Note that if you'd like a dark color, you'll probably need to make other changes too, or the text won't be very legible.

Dashboard > Appearance > Background

Hopefully my last question: I'm still confused about .comment-reply-link and .comment-edit-link

You said that I should write it as "a.comment-reply-link" whereas everything else has looked something like ".entry-meta a". So in this case, how would I set visited and hover commands for those selectors? For instance, let's say I wanted comment reply links to remain black all the time, would I write the code like,

a.comment-reply-link, .comment-reply-link a:visited, .comment-reply-link a:hover {
color: #000000;
}

...or does there need to be an "a" in front of each ".comment-reply-link"? And if that's the case, then how to specify visited and hover?

Thanks again, there's nearly a light at the end of the tunnel and I will have to find a way to buy you several drinks.