Silkies are not easy to sex by the novice until the birds are adults. The rooster has shinier neck and saddle feathers and the wattles and comb is more pronounced.
What do you mean with that the smaller one is not as colourful... a black silkie should be black. If you mean the lack of feather iridescence than it could be that that is the hen, although some are slower to mature than others even from the same clutch. The hen should start laying at about 4 month.
Hope this helps.