Certain colors or color combinations appear different on Mighty (vs. other browsers). This is due to color compression and the lack of "crispness" is more impacted with the color red - often when there's red text on black backgrounds or red backgrounds with text on them.
Unfortunately, we don't have a perfect fix for this quite yet, but it's a known issue.
If there are situations where you want perfect color, we do have a bit of a buried option but we don't advise having it on all the time since it will use a lot more bandwidth and might add more lag to Mighty:
Please let us know if this is extremely high priority for you, as it will help us prioritize against other issues.