Nicolas Cannasse has gone ahead and added variables to CSS. There have been efforts earlier to improve CSS, like CleverCSS and Sass. However, by adding variables Nicolas has perhaps lightened the argument of non-semantic CSS names in CSS frameworks. Reusability tends to create non-semantic names, and having variables to reuse values will help us skip the non-semantic CSS names. Instead of using CSS class called halfwidth, now we can have a variable and use it whenever we want to set width to half width. A good way to centralize certain code, avoid non-semantic CSS names and in the process also reduce some HTML markup.
W3C has repeatedly rejected the color module. The reason perhaps hovers around the conversion of a CSS document to script, which I think is a completely valid reason. But if such efforts as that of Nicolas’ gathers support, it can get popular very soon.