I have some fry at moment that are a month old and still no signs of colour, it can sometimes take some time before thier colours start to come through.
Their only just over 4 weeks, you should see black developing if their have any from about 3-4 weeks, the other colour can take another 3-4 weeks to develop.
Not like mollies or platies when it comes to that. The platy fry seem to show a hint of adult colors by a month old and the molly fry show non-silvery colors quite early in their lives.