Gravel and YB are in the same complex called the super stripe complex.
When two genes are in the same complex, they act like a super when an animal has two of them. That means that every offspring from that female would pass on one of the genes in that complex to their offspring, but never both unless the male is also carrying them.
That complex also means that your Ivory cannot be gravel because Ivory is a super yellowbelly.
If your female is YB and Gravel, she’s actually a highway, not ivory.
Gravel and YB are very difficult to ID one from the other. You need to either test breed them or have them shed tested to find out.
I would get an male that is definitely gravel in order to make highways.
But do remember the BP market is very saturated at the moment so selling can be difficult. Also make sure to have space and a reptile specialist vet lined up in case of emergencies