You have some beautiful cobalts and they will brighten up even more as they grow. What kind of supplements are you using? Some supplements have pigments that help keep the frog's natural yellow or red coloration that can fade over time. But, I have seen people overdo it on the pigments. I once saw a photo of an orange/red leucomelas. It was pretty, but very unnatural.
More importantly, and you probably know this so forgive the unsolicited adivce, dart frogs need supplements, especially calcium, and most dart froggers alternate supplement brands. I use calcium powder several times a week and then a vitamin supplement weekly. I have a separate pigment enhancer for my orange/red frogs (Pumilio Cristobals and Imitator Intermedius). Sometimes I simply use Paprika in place of the pigment enhancer. It works well and it's cheaper.