Frog is a mob that turns other mobs into building blocks. Frogs flick out their tongue at small slimes and small magma cubes and swallow them whole: a small slime eaten this way leaves a slimeball behind, and a small magma cube leaves a froglight, a full-brightness block that exists no other way.
Which froglight you get is decided by the frog, not by the magma cube. A temperate Frog produces ochre froglight, a warm one pearlescent, and a cold one verdant. The variant is set by the biome a tadpole grows up in rather than by its parents, and that is the whole trick to collecting all three colours: scoop a tadpole into a bucket, carry it somewhere warm or cold, and let it mature there.
Breeding runs on slimeballs. Feed two adults and one of them lays frogspawn on the surface of water; the frogspawn hatches into tadpoles, and tadpoles are a separate mob rather than baby frogs — they swim, they cannot breed, and they die out of water. Frogs themselves follow anyone holding a slimeball and take a lead, so a herd can be walked to a base instead of shipped.
Frogs cannot be tamed, and they jump high enough that a frog enclosure wants walls rather than a single fence. They only eat the small variants, so a large slime has to be cut down first, which makes a frog a tidy finisher on a slime farm — the slimeballs it produces come out of mobs you were killing anyway.