Sorry for a possibly stupid question, but it's a bit hard for me to imagine (I tried some visualizations and I'm still not sure what exactly the problem is - or possibly what checkboxes in particular are we talking about).
So - with red/green colorblindness, you don't see the (green) checkbox on the dark grey background in Avast? (is the difference in brightness too small, i.e. is the green to dark or grey too bright)? What changes would make it better?