Indicator light on combinator

[McDuff]

TL;DR, what, and why

A settable coloured LED on combinators so that you can see what's going on in your programs.

That's it.

Use cases

Set all combinators on a particular circuit to one colour so you can follow the signal path.
Set all combinators that do the same thing to the same colour so you can find them in big banks of combinator logic without having to trace the difficult-to-see wires.