Thanks for the responses guys!
Dominik, really appreciate the advice, I am aware that in houdini it doesn't really matter what format it is in as they are all vectors regardless, however importing these into Maya as an alembic seems to fail unless they are in the format rgb. I realised I was approaching the attribute create incorrectly, so instead of setting the type to vector, the correct approach as you said would be to leave the type as a float with the type qualifier set to color, then increase the size to 3. That all seems to work perfectly with that set up, so thanks for pointing me in the right direction.
Henry, the setattribtypeinfo() type info also worked a treat for switching it once it had already been created, so thanks for that too!