Testing colors

[Latropos]

Summary

Improve experience of creating new tests of colors, reuse logic to normalize color instead of requireing passing them in unified form.

Test plan

• The tests don't crash when you provide color that isn't hex (like rgb(123,45,67) or yellow)
• The tests don't pass when you provide invalid color (like 123456 without "#")

[szydlovsky]

Looks good, nice improvement!