Good question. There are 'brassy chins' that have that yellow tint as juveniles, which usually molts out as they mature. There are two other things to look for in chinchilla-line rabbits:
1) Chinchilla is simply chestnut agouti/castor genetics, with the chinchilla c(chd) gene that removes (all or most of) the yellowish tones, replacing yellow/orange/fawn/red/cream with pearl white. Where most agouti rabbits have a yellowish triangle on the nape of the neck behind the ears, chins have a pearl white triangle.
2) Chins often have gray, blue-gray, marbled or even bluish eyes. When looking at the eye of your brassy kit, it looks gray, not brown like a normal full-color agouti.