Well not necessarily. The BS4343 standard on which these connectors are based defined several voltage bands which were designated different colours and also differentiated by having the earth pin at a different position based on the clock. Each voltage band was also available in 2 pole, 3 pole, 4 pole & 5 pole variants as well as 16A, 32A, 63A & 125A ratings. The most common ones we see here in the UK are '6h' (ie. earth pin at the bottom) Yellow, Blue & Red, with Yellow used for 110V, Blue for 230V single phase & red for 400V three phase.
The colour band denotes the maximum voltage present in the connector, so, a 208/120V supply (ie. The US standard of 120V L-N & 208V L-L) would, correctly, use a Blue 5 pole 9h connector for a 3P+N+E supply. We use exactly this arrangement in our factory & I've also seen it used in several UK Universities. Its thrown the odd contract sparky who assumed that the socket in-front of him was a 'standard' 3P 32A 230V socket.....
Mmm slight confusion there, should never see a 6h yellow (see below) or 3 pole red.
In my experience (which I don't claim to be the difinitive situation) in the early days most of the connectors had adjustable inserts so the earth pin could be in any of the 12h positions. It was quite normal to have equipment racks plugged into dedicated sockets and the first in the suite would commonly be 1h and increase by 1 along the suite.
I'm not sure about this point but I believe theses originated in naval situations and coming ashore (so to speak) there was initially some confusion where the major key should be and as such some confusion where 12h was. I know we now have 12h at the hinge and the major key opposite so that is fixed.
Moving on they settled on some 'standard' layout's, for example:
All yellow 4h (except I've dealt with some 5 pole at 6h).
Blue 3 pole connectors 6h but 9h for red, 4h for yellow.
Blue 4 or 5 pole 9h (upper limit of 250V so should not used for UK 3ph)
Red 4 or 5 pole seem to have standardised at 6h but 3h or 11h for non 50Hz (VSD) or over 420V (lots of confusion exists on these so tend to stick to 6h)
The colour does denote the voltage bands for use and that also gets very confusing, this is from memory so please excuse me if there are errors or updates. The voltages are designated in fairly narrow bands with gaps to the next colour, something like Purple = <25V, white = 40-70V, Yellow= 100-130V, blue = 200-250V, red = 300-460V, black = 500-1000V. There has always been confusion which to use for a voltage in between.
Current rating are up to 800A and pin configurations up to 7.