I couldn't find lime sherbet, so I used mint chocolate chip for the green part. I found that the easiest way to line the springform pan with the first layer (of green) was to open the (rectangular) ice cream box & cut a piece (the thickness that I wanted the green layer to be) and then cut it in half (so that it was the height I wanted the cake to be)... I used 4 of those pieces to go around my pan.
I did the vanilla layer the same way. Then for the red part, you mix the chocolate chips in & fill in the rest of the cake. (Can you tell from my picture that I forgot to mix my chocolate chips in- I got a little too excited & skipped that step, so I just stuck them on afterward ;)
I was really happy with how it turned out! Isn't it cute? :)