good question but silly one as well lol. Remember - bee sees things in UV spectrum. We don't give off much UV spectrum because we're not photosynthesis-based organism. Plants are so they give off certain spectrum. Let me show you what the hell am i talking about -
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Left = human's eyes | Right = bee's eyes
They are attracted to darker color. The darker it is, probably the juicer. That's why you always hear your mom telling you and you telling your kids - wear lighter color clothes when you go to picnic!