Chick feet tend to start out this sickly grey-green colour and as they eat more and more wild birds they yellow up. Times vary from chick to chick too. Chicks in captive breeding programs tend to have lighter coloured/grey-green coloured legs for longer because they are fed domestic birds - chicken/turkey/domestic duck will keep they grey-green, japanese quail is sort of somewhere between wild and domestic and there is some change with that. But its the wild stuff that really makes the legs/feet go that violent yellow they have as adults. Captive adult birds legs tend (general statement) have lighter yellow legs because of their diet.
Short answer, don't worry, they'll go yellow ...
