Ofcourse, afterall, everybody knows DBZ was based off of ESF.
Get a clue: Goku was just as powerful as Vegeta. He could have power struggled Vegeta's Final Flash...
IF he ever shot it, which he didn't.
It's pointless to really argue about this. There were a lot of mistakes made in DBZ, so really it comes down to personnal preference.... Some may go by the first time he called it out, some may go by the rest of the times, some may go by the games (in which case, Final Flash should be blue...), but if you were really so gung-ho about it, why not ask A.T. himself?? He's the only one that could really give an official answer....
It's doubtful this will ever be changed, but if you actually think it NEEDS to be changed, you can simply copy the ki blast attack sprites, delete the big bang attack sprites, and then rename the copy of the ki blast sprites.... It's that simple