Okay, your logic is a bit off. If you pair a Pastel Yellowbelly and a Spider together, you get a brighter yellow Bumblebee. It's called a Bumblebelly and it was done last year.
You don't necessarily get a BRIGHT yellow anything with a Yellowbelly. It just changes the tone of the animal that it is paired with. So your question is, would the spider progeny be bright yellow when paired Spider with a yellowbelly??
Not really. Just a lighter animal.