Language entry name is DSPLYMNU_NOINVERTMAP
This pull request adds a new CVar called "cl_disableinvertedcolormap" which when activated changes the Invulnerability Sphere colormap from inverted grayscale to a tinted grayscale (deep blue to pale yellow). This is designed to make it easier on the eyes.

Many source ports have their own variation on this - GZDoom seems to be the only one that forces you (without mods) to endure this harsh on the eyes colormap. Also - even if you have a mod that changes the invulnerability sphere to something more eye-friendly, another mod can override it with an inverted grayscale colormap of its own, so this is meant to address that on a more fundamental level.
Pull requested because I am not sure if there is a better way to do this. I admit it's a hack.