OH, I see what you're saying.
Spawn A1- Yellow Dragon x Black = Betta 1
Spawn B1 - Yellow Dragon x Black Marble = Betta 2
Betta 1 x Betta 2 = ??
Well, keep in mind that there is no defined gene that creates the yellow color in bettas. It's only a phenotype- it's the red gene in disguise, and that disguise is NR (nonred.) This causes the less dense red, which reflects yellow in the phenotype. Yellow x yellow will never = yellow, it'll throw mostly reds, blonde reds, oranges and MAYBE a yellow or two.
Black, on the other hand, is a result of a mutated gene which conrtols the density of melanin in the geno/phenotype. Black x black = black. (Assuming the mother isn't a melano homozygous genotype, which are infertile.)
The result of crossing a red(the yellow in disguise)/black with a red/black marble would be a dark-bodied marble, with (give or take density, it'd vary for each fish) red wash. Marbles' genes will hide some layers and reveal others, however, so you might get your goal of a yellow & black marble.
Really intriguing stuff, you should try it just to see the outcome.