Composting Cavern

When Composting Cavern enters the battlefield,
choose one or more colors that aren't red or blue.
Then sacrifice it unless you pay 1 life for each
color chosen.
{t}: Add one mana of any of the chosen colors.
Whenever a creature you control dies, you may
exile Composting Cavern. If you do, return that
creature to the battlefield tapped under its
owner's control.