pick a color

So why aren't you getting her a bracelet instead? Getting a backpack for your birthday seems akin to getting something like, I dunno, gym socks. Yeah it's practical but it's not very fun.

she's been mentioning how she loves this particular backpack ever since i started talking to her

Oic. So why not ask her straight up which color she likes best? Yeah you'll give yourself away, but at least you'll know for sure that she loves her present. If she's particular about this style of backpack she might also be picky about the color.

because i am a black belt in the art of surprise, throws

Purple? Chicks like purple.

Second.