Speaking from memory, i'm pretty sure that you aren't (weren't) allowed to wear a dark blue shirt with a V neck, as the V neck has to be worn with a tie and you can't wear a tie with a dark blue shirt. It may have changed!
At the time it was a complete balls up,this was just after the V necks came into service in the early/mid 80's & the was a lot of pished off people who wore dark blue shirts & were 'forced' to trade them in for light blue,stores had kittens due to the amount of exchanges so the staish then made said in SRO's that we could,then shortly after the dress reg was ammended.Said chimp we had at the time tried to enforce the order that was ammended by the staish!
I do know the local a&n store made a roaring trade in round neck jumpers!