That is what I thought. So that means that the down colour was not an indication of sex in my case. They were exactly like the OPs chicks, one with a very well defined V on its head, continuing down its back and with well defined eyeliner - now a cockerel.
Due to imperfect genetics, there can always be an exception which is why even experienced chicken owners will be uncertain on the rare bird up until the point where it either crows or lays an egg (and even the crowing is not absolute).
)
The really annoying thing for me is that they were from eggs that I had bought as Marans. The seller had the pens of both breeds near to each other and sent me the wrong ones - and now they turn out to be cockerels - reverse lottery win...