My belief is that when they filmed the Floyd-visiting-the-Monolith sequence, there were no keypads. When Kubrick moved on to filming the Discovery scenes, either some of the silver lunar suits were modified, or new suits were built. In any case, the Discovery spacesuits have sleeve keypads, which were all yellow-orange (even on the blue suit which hangs in the Pod Bay).
Then at the end of the shooting Kubrick needed silver suits again for the "astronauts on the surface near Clavius" scene, so at least Keir Dullea's red suit was painted silver (but it still had its arm keypad).
This suit has been exhibited, and it appears to now have BLUE keys. So I guess this was changed when the suit was repainted, or after filming at some point.
Pic from my files
I note that the "IBM" Is just written in Helvetica, it's not the distinctive IBM logo. So maybe the whole thing is fake, who knows. :lol
For "2010 the Year we Make Contact", a 2001-style suit was recreated for Keir Dullea to reprise Bowman. I consider this a replica because, like everything else in the sequel, it was recreated by analysis of film frames, and not by directly copying the original props.
I consider the other space suits seen in the sequel, the US and Soviet suits, to be horribly banal and boring, looking just like off the shelf 1980s Shuttle era space suits.