I agree with nikki.
I find the best cosplays come from a more realistic color of hair for your wigs. Especially with blonde, naruto for example many people go bright highlighter yellow, however i think it looks better with just a more natrual looking blonde.
I believe the same would go for roxas, hes style is a bit more realistic than some anime characters. Hence why his hair color should be more down to earth, even if its spiked upwards.