Nothing stopping you from creating .green, .yellow classes in the stylesheet, if you want to color the text displayed in the final document. See
http://www.w3schools.com/CSSref/pr_text_color.asp
for details. Click the try it yourself button to see how changes will look prior to committing it to your document, if you are uncertain.
BUT for those of us with e-ink readers, please preview in one. Some orange will just disappear completely against grey, etc.
If you just want to color your code for easier readability see my previous text.