So in order to reign in spring this is what I made
I used skewers (that I was too nervous to cut to hold it up)
Next time I make a cake over three layers, I'll use dowels. By the end of the cake cutting it was the leaning tower of rainbow cake (might have also helped to even out the layers but it was 2300h when I assembled and crumb coated it). Didn't seem to matter much to everyone else *shrug*.
Would I do it again?...yep.
Were people concerned about what I put in it to get the bright colors (only food dye)?...yep.
Did people like it?...yep
People were oddly particular about what colors they wanted to eat and purple was the first to go.
Anyway, happy spring.
(also now I wish it was socially acceptable to plan other peoples' kids birthdays so I could throw a rainbow themed party)