Extend CSS color support with css-color module

[asamuzaK]

Currently, support for CSS colors is very limited. The css-color module covers most of the colors in CSS color module level 4. However, when converting colors, they are first converted to the xyz color space, which can be a performance issue. So, as a last resort, I added css-color at the end.

Feel free to close if the performance loss is unacceptable.