Can a recessive trait be guaranteed if only from one parent? YB

[Stewart_Reptiles]

So I am looking for a female for my boy and have been looking for a few months now. So let’s say I found one that is a great match for what I’m looking to produce. However the YB is one of the most important aspects to be in her as I am looking to make ivories.

So so the thing is: this female only has YB from one parent, and not from a super yellow belly.
Seller says she is guaranteed YB. Is that possible? I thought YB was a hard genetic to distinguish and I see a lot of “possible” YB snakes for sale.

Please let me know your thoughts on the YB genetics, can you tell for certain that a snake is YB if it only came from one parents side just by looking at its pattern on belly?

Would be super grateful to receive and answer for someone that knows more

YB is not a recessive gene

Yes it is easy to recognise a YB in a clutch VS a normal where it gets tricky and people list something as Poss YB is when other genes are involved, the more gene the harder it is to identify a snake at 100% especially when dealing with subtle morphs.