Welcome Springtime!I am always up for a cupcake party, and the First Day of Spring is a perfect excuse for one!We had intended to make these cupcakes as a St Patrick’s Day treat — sort of an end-of -the-rainbow pot-of-gold Leprechaun thing — but the time got away from us and we didn’t make that deadline.Instead these cupcakes are in celebration of the first day of Spring (even if it does look like Springtime on the North Pole right now outside).They are Key Lime cake with a cloud of Vanilla frosting swirled high and a candy rainbow on top.The taste is light and…