Ich habe meine Kürbisse spät gepflanzt und sie sind immer noch mega-grün … Gibt es eine Chance, dass sie färben?

They’ll be fine. The orange color comes from the lack of chlorophyll, which happens when the vine dies or you cut the pumpkin off. As the plant is, basically, dying it stops supporting the chlorophyll and the natural organe color shows through. Usually takes a week or two to fully orange up. You could cut them off now if you were rushing for Halloween – though some very small and unripe pumpkins will, for reasons I’m unsure of, still stay green and not turn orange.