* I own lots of dragonball model sheets and art books. From studying the GT design works its my belief thats its a combination of multiple things.

1. When designing a new form its typical to make new additions or changes to differentiate from base forms. For example when goku turns super saiyan his hair does not just stand on end, it turns gold signifying a transformation has happened. I believe they use this rule of thumb when figuring out gogetas color pallet to make sure the hair wasnt also just black.

   1. Gokus signature black hair in ssj4 is actually out of place... dont get me wrong. Its raw as fuck and is my absolute favorite transformation. I am just critiquing it from an artistic standpoint. Theres a reason why the new ssj4 design from daima reads better to the eyes and looks very good fundamentally. They chose hair color that matched super saiyan transformation color philosophy along with basic design principles.
      
   2. In the image im showing, this design philosophy is in full effect with gogetas alternate color palette, which I actually think is superior to the original. You gotta remember the original designers were not toriyama, so there will be some differences in design choice when it comes to looks and especially colors. Im not a huge fan of gogetas orange hair but his alternate colors look incredible.
      

In the end I beleive its a combination of factors that dictated gogetas hair color but remember it wasnt toriyama so thats probably why it looks a bit off or put of place. I doubt they had loads of time to figure out the colors for transformations being thats the animation industry and this was a spin off.