Easy enough to adjust the colors if you don't like mine. I realize Red/Green colorblindness is common, but these were the colors that worked best for me.

Find these two lines in the CSS:
.select {background-color:rgba(255,0,0,0.1);color:rgba(255,0,0,1);border-radius:25px;}
.selectG {background-color:rgba(34, 139, 34,0.1);color:rgba(34, 139, 34,1);border-radius:25px;}

Pick two colors you like, find the RGB codes, and replace "255,0,0" (twice) with the first one and "34,139,34" with the second one. (Leave the .1 and the 1 alone - they control the opacity.)

Take out the "border-radius:25px;" (twice) if you like square corners. I personally found it easier to spot pairs but harder to see boundary marks that way.