Hi Linda,
I had to list the parentage again to answer:

[Iris cengialtii x (Iris variegata x suaveolens var. mellita)] X
[('Kupari' x 'Rosemary's Dream') x ('Kupari' x suaveolens var. rubromarginata)]

So...
Iris cengialtii - relatively blue, no yellow
Iris variegata - definitely has yellow
Iris suaveolens var. mellita - a rusty purple, most likely with some yellow in it
Iris pallida 'Kupari' - white, no yellow
MTB 'Rosemary's Dream' - pinkish purple on white ground plicata
Iris suaveolens var. rubromarginata - same rusty purple as mellita

So I'd say the answer is yes! There were several sources of yellow.
But what exactly is going on pigment-wise in this seedling? Maybe your petal soaking methods would help to start figuring out. Unfortunately it's too late for this season.
Maybe next year.
Best wishes, Tom

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Thanks Tom. Definitely redder than pallida. Do any of the species in
the pedigree have yellow? I get so mixed up about the various pigments,
esp the various shades of purple. Never can remember whether they are
different anthocyanins or a mix of antho & yellow or a mix of antho &
other stuff.

Linda Mann