This color system for marking and identifying queen honeybees is accepted
and recognized internationally by beekeepers:

White (or gray) is used for years ending in 1 or 6.

Yellow is used for years ending in 2 or 7.

Red is used for years ending in 3 or 8.

Green is used for years ending in 4 or 9.

Blue is used for years ending in 5 or 0.

I have coined a little phrase that I find useful to help recall the sequence
of years and colors:

What Year is on the Royal Girl's Back?  for White, Yellow, Red, Green, Blue.

Does anyone have a Yellow or Red marked queen still working anywhere?