My K is in platinum. You can set it in any metal you want. I don’t see a cup working with your stone. If it has a cut issue, then see if it can be fixed by a cutter. I really can’t see what you mean from the pictures. The antique asscher is K. It really isn’t that much different than the round I color stone.
I know people always say white settings = whiter stone. I respectfully say... sometimes! I think if a stone has a hint of a tint that a non-white metal actually makes the stone look brighter (thank you, contrast!). I have a J colored ACA in unplated 14k white gold. I think the contrast makes the stone look dazzlingly bright.