As has been said, depends entirely on the unit CO/RSM.
I served at units where it was worn, and units where it was the green thing / 58 Pattern if you were a SNCO. And don't get started on sleeves up/down - un-tucked/tucked in malarkey, that's an entirely different can of worms!
I will say though, I was at one particular Regiment where un-tucked was in fashion, and one of the SSMs loved nothing more than gripping the lads for not having their stable belt on underneath their un-tucked shirt. Yes he was a bit of a knob!
Wait and see!