So simple it's barely a Mod.
Just changes the daylight HUD colour to Black, much easier to see what's what.
Otherwise drop the new HUD_init.lua file into DCS_World\Mods\aircraft\A-10C\Cockpit\Scripts\HUD\Indicator\
N.B. Always a good idea to make a backup copy of the original file first. ;^)
Koz's A-10C Black HUD Mod