Which issue, if any, is this issue related to?

See:

• [parser] Implement full featured CSS parser css-parser#2
• Fix performance of constructor parsing rules #6869

Is there anything in the PR that needs further explanation?

• added a fast abort for all color-* rules
• added some utilities in support of the color-* rules
• ensures that regexp's in utilities are declared once and then reused.

I don't mind splitting this up into multiple PR's, one for each rule, but the changes are all similar and minor.

I am unsure what the preference is in this project for balancing the extra noise and review work of multiple PR's vs. the clarity of small chunks. I didn't want to open ±10 PR's without prior discussion :)