On 9/11/2019 4:23 PM, Ian Jackson wrote:
In message , S Viemeister

Our bins are blue for recycling, and black for landfill - flies
congregate on the lid of the blue recycling one, and ignore the stinky
landfill one.

I think flies' eyes are particularly sensitive to the blue end of the
spectrum. Don't electric fly zappers have a UV neon tube to attract them
(looks blue to us humans)? I painted a garden seat with Cuprinol Sage
paint (which is a somewhat bluish darkish-green colour), and it often
was covered with flies.

Hmm. I painted three garden benches with blue paint (marine/royal)- I
haven't noticed flies congregating on them the way they do on the
recycling bin, which is a lighter, very bright, blue.