post a pic.
were your parent yellows clean? That means they did not have bars on them (usually black or grey); no wash out in the colour. yellows are supposed to be (in the trade any how) bright yellow with the black band on the fins. no other colours at all.
newly hatched yellow - (you normally wont see them this small, as they are in the mouth)
Good yellows -
Smidey on here, also has some beautiful yellows (or had).
Occasionally juvi yellows will have some faint bars on them, but normally they are clean. depends on what the parents are like.