Your blog is private, so it is hard (well, impossible, to be honest!) to diagnose your problem in specific. However, it sounds like what you have done is change the color via a "global" css selector.
A big key to understanding CSS is the final specificity principle: The last most specific rule is applied. A brief example:
Let's say you have two CSS rules such as
body { color: blue; }
p { color: red; }
Here, all text will be blue, except text inside paragraph tags, which will be red. If you want some things to be green, you could assign a class, to make more specific rules:
.green { color: #0c0; }
p.green { color: green }
The first rule would specify a mid-tone green, for anything with class="green"; the second more specific rule would specify that a paragraph with class="green" would be a bright green. Since this is a more specific rule, and, as it happens, is last in order, that is the rule that would apply to paragraphs.
More info than you asked for, but the gist of it is, sounds like your rule isn't specific enough. Hope that helps.