Not sure what it is, small seedlings tend to look somewhat different. I’ve gotten a few such seedlings with yellow leaves, but here they tend to die slowly. Yellow leaves tend to scorch in full sun and the plants grow slowly. If you’re looking for an arietina (not mascula ssp arietina), then perhaps you could try P. arietina ‘Northern Glory’ which is particularly nice. Pivoines Rivière has it, although I don’t see it listed this year.