Neurg, Tectonic Mind

(Neurg isn't a spell, it's affected by summoning sickness, and it has "{t}: Add one mana of any
color." If Neurg is your commander, it may be played from the command zone, it's affected by commander tax, and your starting deck may contain cards of any color.)

Whenever a land creature you control attacks
or blocks, add one mana of any type that land could produce. You don’t lose this mana as
steps and phases end.