Customization > Colors (see
help file)
Change the Color Category drop-down to "Rules", change the "Markers" color.
I'm trying to find the ruler background color... what the heck are they calling it? Can it not be changed after all? FFS.
OK. I'm wrong. In X3 you can't change the ruler background. Chalk up another victim to the "50 Shades of Grey" fashion cult.
I guess my reply is still valid - you can change the color of the marker text. You just can't change the color of the background in order to maximize contrast.