If Trunks went SSJ4...

[Southern Gothic]

Would his hair be black? Legitimate question.

 

[Goddess Ultimecia]

I like to think that they keep their respective hair colour, Goku had black hair as a SSJ4, Vegeta had a brown shade of hair. Gogeta had... well... umm... He has red hair but I guess this can be rectified if Gogeta's a natural red head.

Gotenks' hair colour would interest me the most honestly.

 

[Southern Gothic]

That is true that none of the SSJ4's have the same hair color. Odd in a way. Wouldn't be surprised is Trunks stayed purple.

 

[SSJ2]

I think it would look kind of like Base Gotenks' hair colour scheme.

 

[Captain Cadaver]

I imagine it'd be a very dark violet shade, enough to keep to his own original colour whilst differing enough to show some change, much as Vegeta and Gogeta's did.

 

[Let's Go Fearless!]

How about like this?

 

[Southern Gothic]

I do imagine his fur being slightly different for some reason. Just a slight shade off, maybe cause he's half human.

 

[kriss-]

Trunks seemed to have a unique hair color like his self in the current time-line. Probably because he is a hybrid and his hair doesn't 'have' to remain the same length throughout his life. So his hair would probably remain the color it is in his current Base form.

 

[Southern Gothic]

He does indeed have a more unique look compared to most other Saiyans/Half-Saiyans

 

[Sam]

I think that Gogeta, ignoring idiotic GT logic, had the red hair, perhaps because he was a fused being?

As for Trunks... yikes. I have no idea. Toriyama said allegedly that he didn't make a female Super Saiyan because he didn't know how they would look. I would say the same for Trunks if I had to figure that one out lol. I think his hair would either turn black, or be like the image above. SSj4, does, after all, seem to bring out the more primal instincts of the Saiyan, and all pure-blooded Saiyans all have black hair. It could be that the transformation overwhelms his natural hair color.

 

[Papasmurf]

I'd assume it'd be a dark lavender, but no way to know until DB Heroes decides it's time to make SSJ4 as cheap as the previous forms, a process that's already begun with Broly and Gohan.

 

[Goddess Ultimecia]

To be fair Gohan and Broly are hyped up in outside material to have monstrous potential/dormant power. It seems only fitting that they'd acquire the form that brings it all out on a whim.