Another way, which is not always popular. Is to breed your bird to a known normal, then breed the young back to the possibble split parent. Of course this does not work as well because even if the parent is split you don't know for sure that the young you use got the gene.
Was talking to a friend yesterday about when he first had silver quail turn up in his avairy's about 20 - 30 yrs ago when they were rare. He was gobsmacked, cause he had only bought normal brown kingys and bred them to each other, and all new blood was also normal brown.
But as I explained
BB x Bs where B= dominant brown and s = recessive silver
BB x Bs produce BB, BB, BB, BB, Bs, Bs, Bs, Bs
Next Generation you add in BB's you still get those splits, and as long as you keep one of the splits you still have it and if 3 or 4 years later you happen to put 2 distant cousins together and they happen to be splits - Bingo
You never had a silver but you always had the gene.
Same applies to all the finch splits.
LML