my fantail fry at 1 week was less than an inch long
they usually dont grow much in one week
after about 2-3 months then you can really get some
differentiation in size( especially the runts)
however my fantails fry arent doing so well compared
to my comets- but that was totally expected
when do they get colour?
it really depends
they can start getting colour in a month
near the spine and along the fins
but for them to look like their parents it can take
a few month to a year
and also some of the fish dont get colour at all
they remain brown all their life - but i havent come across this yet
you can put them in after a few months usually
just make sure that the current isnt too strong
your have to judge really since you'll know how good they can swim

and keep us posted