We really love to harvest our Calamondin (or Calamansi) as they start to turn color. Much like the limes that are harvested when Yellow green.
It is a type of hybrid citrus, a hybrid between kumquat and a mandarin. Calamondins make excellent souring condiments, used like lime or lemon. It has unique aroma and flavor. It is excellent for making pies, like key lime pie, but instead, substitute Calamondin. Makes excellent refreshing drink, use it instead of lemons. It also makes excellent jams or jellies. Yeah, it makes excellent wine too, at least our Calamondin Wine was a Double Gold Medal awardee at the California State Fair in 2010.
It develops deep dark orange color during the winter when the skin becomes sweet and edible like a kumquat, but loses some of its tartness, but then it would make excellent marmalade.
We also use the unripe small green fruits when cleaning our hands as it removes the smell of fish and other nasty smelly stuff by crushing the small fruits and rubbing it into our hands and fingers.
It is not commonly available from the stores in the US even in Asian grocery stores, it is rare. So we grow our own, lots of it. It is graft compatible with all kumquats, after all, it is a mandarin and kumquat hybrid. It is also graft compatible with some mandarins. Not graft compatible with grapefruits and pomelos.