I recently acquired Dominion: Prosperity (yay Christmas) and came across the Platinum and Colony Cards which are designed to be new Basic Cards (like Estate, Copper, etc...).
My question is, should I (or do you) always play with Platinum and Colony even when you're not using Prosperity kingdom cards? Or do you only play with them if you're doing a Prosperity only game? Or do you use them whenever some (or certain) Prosperity cards are chosen as kingdom cards but otherwise you leave the Platinum and Colony to the side?