Of course, they key thing is to have a shirt that looks unlike anyone else's.
I had a couple of soft SD shirts from someone called Stefan Hartounian - but I can't google him anymore (10 years ago).
If you are wearing the whole Ginger Bollocking Suit in the bizarre, foul, 22oz cloth that was favoured by the RA Dress committee then just wear an egyptian cotton beige or cream shirt underneath the jacket as it is much cooler. No-one ever noticed for me.
Nor did they notice the shiny, strappy RAC brown boots as opposed to the Barnardo's corrective brown barges. If you are wearing such boots you need never worry about the right kind of socks either...