CSS is a powerful tool. However, as you consider accessibility issues it is important to implement it wisely and take care to assess the ramifications of your decisions. Using CSS to separate content from presentation remains an essential concept to keep in mind. Remember, too, that using proper semantic markup and aligning visual layout with reading order help assistive technologies to offer a predictable reading experience for end-users. Using native HTML markup for heading levels, emphasized text, list-bullets, etc. can also help you streamline the use of CSS across your site.
As the WebAIM article, CSS and Accessibility, emphasizes:
The end user always has ultimate control over the styling of a page they view. For accessibility, we need to define accessible styles, but also allow flexibility in our designs for end user customization. The idea that web developers and designers have control over the display of their content is an illusion.
CSS not only helps you as you design and code your site's "look and feel," but it can also help:
Some areas to consider include:
Turn off style sheets in your browser, read through the page, and be sure that an appropriate reading order is maintained. Also, can you understand the page when color styling is removed?