It can be any colour you want.
I suggest that neither IR nor UV are good choices as you can't see them
![Smiley :)](https://www.machsupport.com/forum/Smileys/default/smiley.gif)
White is attractive but white LEDs require about 3.6 V, which is not going to work too well when you are checking 3.3 V logic chips. They might work, sort of. Red LEDs require about 1.2 V from memory.
Logic probes are much faster than multimeters, plus you can leave a few LEDs in the output screw terminals for a while.
I have some test boxes which consist of a numbered row of Red LEDs with a multi-core cable ending in a selection of Ezy-Hooks. I colour-coded the Ezy-Hooks to the resistor colour code. Hook the clips up, jiggle Mach3, watch the pretty lights flash.
Cheers
Roger