I am making a pink and purple tiered cake with accents done in green. It is for my 2yr old nieces birthday next week. My sister wants strawberry cake on the bottom iced in purple then white cake died purple on the top iced in pink. She wants the fillings to match the cake. I figure I could use strawberry jam on the strawberry cake (will that taste ok?) but what can I do on the purple cake??

blueberry?? I don't really know but it sounds like a fun kids cake.

Why not blueberries and if its not quite the color your looking for you could add a bit of purple food coloring. Also you could add a bit of grape jello to butter cream. For the strawberry, I would add the buttercream or any other cream base to the jam.

Adding Kool-Aid to BC is another idea. I did that back in June for my daughter's birthday cake. She chose cherry and unfotunately I hate anything cherry, so of course I didn't like it, but all the kids and adults at the party loved it! A few were even asking me how I made the icing. I would imagine you could use fruit flavored Kook-Aid (do they have a strawberry one? Probably, I guess...). Just a suggestion.

what if you get like a one of those 1-2 lb. sleeve fillings, a white one like coconut and then just mix in some purple food coloring...not sure if the kids like coconut or not...
you siad you were going to use strawberry jam for the pink filling...why not grape jam for the purple filling?...grape jam and white cake seem like they would taste good together...