It’s critical that you feed them bbs once they start free swimming. However, if they are in a well established tank, most will probably be able to survive for a little while because they can always find these micro organisms to feed on. Sorry to say...but you might have lost all of the blues from this batch as blues don’t compete well against their non-blue siblings. How often a WC is done depends on the tank you use to keep them in and your feeding schedule…I do weekly 40-50% WC while keeping them with their parents in a 40 breeder until I sort them out in about 4-5 weeks. You should be able to tell them apart at the size you described. I’ve posted a few threads about ebjd breeding, feel free to check them out
As far as picture example of how to tell the blues and non-blues apart, try to search through this forum, I think there is a thread name “step by step guide to ebjd breeding”…it should help answering your questions. or I can try to serach throught some old pictures and see if I have some good examples...