It had nothing to do with vegeta turning blue it had everything to do that as a saiyan you should always train and prepare for that time a stronger opponent appears.
Trunks looking all happy thinking he didn't needed to get any stronger because goku and vegetal were blue was what vegetal was angry about. Also even tho he now goes to SSJ 2 he still didn't get the memo from vegeta and cell that if you power up all muscles you loose speed.
He is one step away from SSJ 3, like he was one step away from SSJ 2 when he was fighting cell on roids. Seeing future trunks go SSJ 3 even tho we know that transformation would be dope. But we all know that transformation would do nothing to black in the end so we might get something higher who knows
Trunks looking all happy thinking he didn't needed to get any stronger because goku and vegetal were blue was what vegetal was angry about. Also even tho he now goes to SSJ 2 he still didn't get the memo from vegeta and cell that if you power up all muscles you loose speed.
He is one step away from SSJ 3, like he was one step away from SSJ 2 when he was fighting cell on roids. Seeing future trunks go SSJ 3 even tho we know that transformation would be dope. But we all know that transformation would do nothing to black in the end so we might get something higher who knows