It might be the het clown gene.
I've heard that some people have noticed with certain morphs that carry the het clown gene (ex. spider het clown, pastel het clown), the offspring sometimes come out different looking compared to what the morph would usually look like. Supposedly, some of the het clowns come out brighter/lighter, especially on the head. Kinda like how het pieds can have visible markers, even though they're only het for the gene.
I've also heard that some het clowns come out more "clownish" looking, but I think in your case the gene just brightened your bumblebee up!