For current, yes standard LEDs that are labelled something like 20mA are what you want. What you don't want are LEDs that are labelled "low current" or "ultra brightness".
LEDs don't have a voltage rating, all red LEDs drop about 1.8V, all green and yellow / amber LEDs drop about 2V, it's set by physics. (In fact the 6000 desk there's a circuit in the 688 (the mix amp I think?) that uses this constant voltage property of LEDs.) You can get "LED lamps" that are rated at, for example, 12V, but these are just assemblies of an LED and a resistor.
Here's an example of an LED that would work as a red LED, but there's loads of similar:
https://uk.farnell.com/multicomp-pro/mp006834/led-ultra-red-180mcd-637nm-t-1/dp/3648334Hope that helps,
Andy
P.S. Here's a story about LED types. There was one special desk we made for a broadcaster where they wanted to use the routing matrix to create "mix minus" feeds - so they could have 31 of the 32 LEDs on at once. This would have overloaded the power supply and probably blown the 611 fuses, so I specified low current LEDs for this desk. Unfortunately I somehow forgot to change the resistor value on the production parts list - until one of the Sarahs in assembly came to me and said, totally seriously, "we like these high brightness LEDs"! I probably went as red as the LEDs...thank goodness Sarah happened to mention it, I don't think those LEDs (or the fuses) would have lasted long...
