That's a nice thought! Last year I used a creme egg box for Hector's cage (I had to eat all 5 myself before I could've it. I know, selfless right?
) and I had a mini egg mug that came with an Easter egg in with Cleo. You could check out charity shops for cheap mugs and egg cups? The coloured bendy bridges are quite jolly for adding colour. Or maybe a bit of coloured carefresh on top of your normal bedding. And as CMB said, decorating the outside of your cage will instantly make your cage seasonal. Just be sure your hammy can't get at anything if it's not hammy safe but a string of Easter bunnies cut out of paper would be a cheap instant Easter decoration or eggs cut out of patterned paper.