All animals will color up at different ages. Just when you think they have their "forever" colors, BAM! surprises come. That is part of the enjoyment of a chameleon, they are like a box of chocolates...
Yes Nick is 100% right! He will keep changing so don't worry. Typically the black bars will disappear by that age but each chameleon is different and depending on his environment he might just be holding out on showing you all his colors just yet.