On chess.com, the text color for rating changes (like the green “+10” or red “–8”) isn’t something you can directly customize from the standard Settings menu. However, there are a few ways you could work around this:
1. Check Themes/Board & Pieces Settings
Go to Settings → Themes (or Board & Pieces).
Some themes adjust text visibility slightly. For example, darker or simpler themes usually make the green/red text stand out better.
If you want to keep “Nature,” you might try pairing it with a darker board color.
I recently tried the Nature background and enjoyed it quite a bit, however, the following screenshot should indicate why this background might be a bit of an issue:
Don't worry, if this looks like a normal rating picture to you, then you're helping me out by proving my point! 
If there could be some way to edit the rating increase text colour so that it does not blend in with similarly coloured backgrounds, that would be great.