Wasn't J's hair white at some point or am i confusing it with another story?

yes, his hair was white after he came out of the rift, but everything is explained at the end, so I don't want to spoil it.

Short version is that the rift he was trapped in caused his hair to turn white, before then he had the color he dyes it to.

i was hoping he'd stop dying it tbh the white was cool asf

Don't worry, he eventually gets the white hair back after some time