But we don't know if there has ever been a homozygous spider or what they look like.

You’re pretty safe assuming your bumblebees are only het for spider.

I think the confusion here is coming from the relationship between spider and pastel. There apparently is none. The production of killer bees proves that spider and pastel are two different genes and as early and often as killer bees have been produced it sure doesn't look like the two genes are near each other.

So a bumblebee has the spider mutant gene paired with a normal copy of the spider gene and the pastel mutant gene paired with a normal copy of the pastel gene and it passes or doesn't pass those to its offspring independently. So, just as both parents could give the normal for spider version of that gene they could also both give the normal for pastel version of the separate pastel locus and produce a complete normal.