Just because the food you eat isn't orange doesn't mean your barf has to be orange.. When the food goes to your stomach it can mix together and create all kinds of colours yuck XD
It could be because:
a) you're eating too many foods with sodium, check the foods you've been eating recently and see if they have a large amount of sodium. My brother used to always eat spicy meat, but it had so much sodium that he threw up like every day x.o
you're spending too much time in front of the screen. (TV, computer, Xbox, Gamboy, whatever) again, my brother.. he threw up last night, infact (xD) and my mom said it was because he spends too much time in front of the Xbox and his head is getting dizzy
c) you aren't hydrated enough- maybe you need to drink more water. Pop and juice doesn't count, you have to drink enough fluids otherwise your body won't have enough hydration, it could cause you to be weak (even if you don't notice) and you'll puke.
Try asking your parents or a doctor. Maybe you could google it.. But that's just my amateur knowledge. It's kind of hard to tell you why you're puking xD
And erm... good luck?