3 months is still young, though. A very common problem with culling out leakys from black project is the color can come in much later, and a genetically leaky hen can be solid black but she will throw leaky sons and a few daughters. Those sneaky hens are the tricky part. Leaky roosters usually will show some color, it can be barely there, just a tiny area on the hackle and/or the wing bow area and with those minimal leakers they can hide that until 6-8 months or even past a year. That is why some show breeders have a rule for breeding only from 1-2 year old birds- after their fullest maturity has been achieved.
The basic problem is there is not a single gene that makes for a totally black chicken. The two common "mostly black" genes are called E- extended black and ER- birchen. Then you need to pile on helper genes that make more black pigment and cover up the 'leak areas' and you finally have a solid black.
It would help a lot to breed the barreds/cuckoos to solid black birds for this reason..
I don't know your localized terminology for e+... the wild red junglefowl color. In the states it is called red duckwing.. in some countries it is called partridge(in states partridge is another gene also called dark brown.. hobby is horrible with consistent terminology).
Crele is barring on a clean red duckwing, no other mutant genes added. You can make a crele looking rooster on wheaten, the hens will look nothing like true crele hens, and often you are very hard pressed to tell if a particular wheaten hen has the barring or not.. sometimes you can guess by her tail being grayer or maybe a vague hint of bar on the primaries or on a random feather somewhere.
Your picture above is simply a 'mixed color'. He does have the duckwing patch which shows the cuckoo used was not pure for black. He may have the Co gene which could explain why he has the buff coloring all over his body. True crele breasts on roosters are solid black with white barring. If you want to use him and only have access to wheatens, use him over PURE wheaten, no Co, no Mh, no nothing else to mess up the pattern.