TTD coverage highlight is not super obvious to see

[xusheng6]

Right now they are highlighted, but for certain reasons they are not visible enough. We should really make it more visible

Also -- we might want to make it configurable, either through the theme system, or through the settings system

[xusheng6]

I think this is just because we are not using the full alpha (255) here:

debugger/ui/ttdcoveragerenderlayer.cpp

Line 59 in f52fbef

line.highlight.alpha = 64; // Light highlight

, and down below