+1
It USE to be blue for sealing water and coolant (thermostats, water pumps etc), red for high temp stuff (anything near the exhaust), copper for super high temp stuff (the exhaust itself), black for oil (diffs, valve covers etc), clear for body and windows (windshields), grey for high torque (I guess things that get torqued hard lol), and green for stuff with friction modifiers in it (transmission and differentials).
I think there is purple now which is specifically for automatuc transmission fluid but I've never used it or had a problem with the other RTVs not working with transmission fluid.
There's also "sensor safe" versions but I've never had a sensor (o2 or otherwise) go bad from using any RTV so I'm not sure what the difference really is there.
I use ultra black for everything except exhaust parts and have yet to meet an automotive fluid it won't seal when used properly.