Unless your going in full Number one's the spats will look out of place, go with the red flashes tho other wise with BW tartan you could look like the man in black.... you know too dark. If it is casual just go with the vest that way you will be smart but casual. Looking good when you playing but not outa place after and as you said you don't want to upstage the host,

Mind this is just my 2 pence worth