I did think of painting the entrances, or a pattern near the entrances, then realised giving clean boxes in the spring with different patterns could confuse them, more especially if I a colony's old box was cleaned out and re-used within the same apiary (bee yard?).
So all my boxes are the same, the patterned landing board stays with the colony.
There was research about how bees see colours, but I can't recall who did it.