Buff is technically not a single gene, but a combination of genes to get a certain color. For two red chickens to produce the offspring above they had to of been carrying a spangled gene. Since the one above is result of hidden gene showing up it won’t ever be as clean and perfectly patterned as chickens bred from parents both showing the spangled genes and carrying the correct genetic code for jubilee. This is because as you can see from the picture it is only carrying part of the gene sequence for the jubilee pattern so it looks pretty close to one, but not quite 100% jubilee. Jubilee like buff is a combination of genes. Colors and patterns can’t be made spontaneously, but the parent can be showing genes while carrying “hidden” genes that are recessive and simply not showing physically. With colors and patterns in chickens it’s not black and white. A solid black chicken while appearing black may have the genetic code for multiple other colors and patterns. A chicken may look red on the outside, but genetically be carrying other patterns/colors as well. Since you mentioned lavender I will bring up “splits”. A black split lavender for example is all black, but is carrying the lavender gene so if you were to breed to another black split lavender you can get lavender chicks even though both parents are black.