Frogs must be tamed and of adult maturity in order to breed.
When breeding frogs, attributes (base color, pattern color, and breed) from each of the chosen parents are randomly combined to create an egg with one of each genetic attribute. Most of the time, the child frog will have colors and a pattern from one parent or the other: breeding a red and a yellow frog will produce a red or yellow child frog, for example, and will not produce an orange child frog. However, the glass base color or chroma pattern color can occur as a genetic mutation in certain pairings of parent frogs which do not have those colors.
The pattern of a frog determines its rarity. Only frogs with a rarity at or below than the user's level can be bred. Frogs of a higher rarity level may be received as gifts from players at higher levels.
Breeding can only be achieved for a fee, but the amount spent to breed the two frogs translates into an equivalent value in experience gain. (i.e. if it costs 63 coins to breed two frogs, then the player will also be awarded 63 XP). The amount it costs to breed two frogs is equal to the sum of the maximum value of both parent frogs, divided by four (rounded down to the nearest coin), i.e. if one frog is worth 382 coins maximum and the other frog is worth 296 coins maximum, then the cost to breed will be (382+296)/4 = 169.5 which is rounded down to 169 coins to breed.
Given that the cost to breed frogs is based on average max values of the parents, it is possible to lose money breeding. This can occur if you breed a low level frog with a higher level frog and the offspring is the same breed as the lower level parent. You can also lose money if the color combination produced is cheaper than that of the parents, especially if a glass or chroma frog is produced.