Originally Posted by Xyex

I remember reading an interview with Toriyama that I belive came out in an issue of JUMP. I think it was part of one of the question and answer segments, actually. Anyway, someone had asked about this, and about the colors of the attacks. He basicly explained that both elements were his wife's idea. She'd told him the readers would enjoy it more if the attack was called, it'd give it more 'force' or something. And the color was added (or in the case of the manga, the very outline of the attack) so as to give the reader/viewer something to see. Ki attacks were originally just going to be invisible, ala the idea of real-world Ki moves.