Your Lavender Orpington does have white/pink feet bottoms, just don't show as clearly in the adult picture.Interesting. I didn’t know this. I’m no expert on either breed, just guessing based on the birds I have. My lavender orp has dark legs, and (I’m pretty sure) dark soles. Her legs are very thick, almost rooster-ish. My lavender Wyandotte has yellow legs and what looks like an interesting metallic overspray on them.
Here are photos of Willow the lavender Orp similar in age to OP’s birds and again as a mature hen. Last image shows Goose the lavender Wyandotte. Hard to make out the interesting color on her legs. View attachment 4092080View attachment 4092082View attachment 4092085