Two co-workers discuss a memo on dress code

— I don't understand this memo from the boss. It says on Fridays we can start wearing casual clothes, but does that include T-shirts?
— No, it doesn't. See here. It says that short-sleeved shirts must have collars. T-shirts don't have collars.
— Oh, I see. It also says no blue jeans. But what about black jeans?
— That's a good question. You should ask your manager.