Abstract of some interesting results in bee preferences from:
Artz, D.R., Allan, M.J., Wardell, G.I., Pitts Singer, T. 2014. Influence of nest box color and release sites on Osmia lignaria (Hymenoptera: Megachilidae) reproductive success in a commercial almond orchard. Journal of Economic Entomology. 107:2045-2054.
"Blue orchard bees had better reproduction in light blue nest boxes followed by red nest boxes and then yellow nest boxes."
"In the nesting site density and nest box color experiment, the number of nests, number of cells, and number of male and female cells produced by O. lignaria females was greatly influenced by the number of available cavities within nest boxes and nest box color. "
https://www.ars.usda.gov/research/publications/publication/?seqNo115=297997
"Si hortum in bibliotheca habes, nihil deerit." [If you have a garden and a library, you have everything you need] Marcus Tullius Cicero in Ad Familiares IX, 4, to Varro.