It is possible that the feet should be slightly pinker than the bills. The bib could be a bit more colorful, too... slate blue to periwinkle (these are bright birds!!!). The aqua line sometimes makes a triangle at the intersection of colors, but not always, given your references. Is the wingtip slightly within the body? I'm seeing ocher there where it should be green. Because they are so brightly colored, these finches look artificial, like the ones I put on the tree at Christmas. I'd add some noise and brush it out so that the green on neck and back looked more feathery and not so perfectly smooth. Just a tiny bit of ruffling. All small points. The birds do look handsome as is. Carolly