Most beekeepers put a paint mark on each of their Queens once they’ve mated and settled down in a colony
Why?
it makes her easier to find when doing an inspection
you know if she’s not the Queen you saw last time
it reminds you how old she is

Queen Colours
Each year has a set colour with which to mark that season’s Queen based on the last digit of the year
1 or 6 is White
2 or 7 is Yellow
3 or 8 is Red
4 or 9 is Green
5 or 0 is Blue