Is it allowed to discard an action card as last card?
If the player only has one action card left in his hand and discards it in his last turn, the game is over. It does not matter which action card (colour choice card, draw four colour choice card, etc.). The action of this card is no longer performed and the points are counted.
The players decide on different rules in advance (house rules). These must be decided before the start of the game and all players must then abide by them.
Special UNO versions have different rules in the game instructions when the last card is played. These should be read up beforehand.