Well, here they are, 3 days old and now visible. They were black when they hatched out but they seem to be changing quite quickly. They're supposed to be black with white stripes, but maybe that comes later - they shed their skins 4 times before they pupate, so that might be their final colour.
The first photo is how they looked when they arrived in their little plastic box. The white eggs are the shells that remain after they've hatched. The grey-black ones haven't hatched yet, but there's still time.
This one shows the size of the box the eggs arrived in :-
and these are the worms :-
They are growing so fast! I'll post another photo in a few days time when they'll probably be twice this size.