To change the color of widget titles, you can add the following to your Appearance > Customize > CSS editor:
.widgettitle {
color: #f00;
}
To limit that to the left sidebar only, you can add “#secondary” in front of the selector:
#secondary .widgettitle {
color: #f00;
}
Change the color code #f00 to a color of your choice.
http://0to255.com/
There are a few different colors of links in the sidebar already. The ones under recent comments are setup like this:
.widget a {
color: #0dd3ac;
}
And if you wanted to change the color of every single link in the left sidebar, you could add “#page” to the front of the selector to make it more specific.