I truly didn't understand how could you get a "ban from Google" for something like this. Google can't control colors on your page.
If you edit index.php that means you apply a destructive change and will be forced to apply it each time when you upgrade this file.
Also, in the most recent miniBB releases we don't have contribution text anymore, we have a little logo icon with the alt text over it like this:
, if you have upgraded from the earliest releases where there was a contribution link with text on it, you may just to replace the tag in the manner kuopassa