I use red paint to mark exclusively as I usually know how old they are by the box/situation they are in, as well as records I keep....
If you want to sell them use the designated color.. but I really dislike the White, green, and yellow. Just blends in with the pollen after it ages a bit.
INTERNATIONAL QUEEN MARKING COLOR CODE
Color Years ending in
White (or gray) 1 or 6
Yellow 2 or 7
Red 3 or 8
Green 4 or 9
Blue 5 or 0
I use RED all the time because it is easy to spot for my eyes. Testers model paint and a grass stem, and as stated, practice on DRONES..