Airbus seems to keep what's on each system mostly the same between different models.
Gear + normal brakes - green
Flaps - green+yellow
Slats - green+blue
Alternate brakes - yellow
Replace 'blue' with 'electric' on the A350/A380.
Boeing calls it left/centre/right by where it's fed from. Except for the A300/A310, pretty much all RATs feed the centre-ish system. Can't guess why the A300/310 RAT is on yellow.
The widebodies have EDPs as primary power for all systems, whereas the A320 has an electric system. That means that while you want the gear on the centre system on the widebodies (so you can retract in case of engine loss), it needs to be on one of the side systems on the narrowbodies (so that it's fed from an engine + PTU from another engine).
This leads to the gear on the 757 being on the left system where on the widebodies it's all centre (because there is enough electric/air capacity to operate the gear).
Seems with Airbus yellow is always right and green/blue swap left/centre depending on which is more critical.