Creatures change color as a triggered ability upon the block being declared.
04-10-2004
wotc
A Leprechaun with Protection from Green can be blocked by a creature (since it is not green at that time) but will not take damage from the creature (since it is green during the combat damage step).
04-10-2004
wotc
The change to green does not end even if the Leprechaun leaves the battlefield.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.