To change the color for links inside posts in the Blogum theme to be red-orange and not underlined, add this to your Appearance → Custom Design → CSS:

.post-content p a span,
.post-content p a,
.post-content li a,
.post-content table a {
	color: #930 !important;
	border: none;
	font-size: 1em;
}
.post-content p span {
	font-size: 1em;
}

The http://happyimpermanence.wordpress.com/ site has a lot of custom HTML inside the posts that change the color of text and links. The example above tries to work around those settings and override the HTML color settings you added to links inside posts. Note that the example CSS may not catch all of them depending on the HTML code. To avoid this problem, you should remove the extra color settings inside the posts using the HTML editor.