I ransacked my fabric stores and turned up some pink linen. It's actually almost exactly the same color as the madder-dyed linen I see here, so score! I admit I was vaguely planning on woad-blue, but since I've already got the pink, pink it is.
This polyester "china silk" looks to be about the right shade of purple. My nearest good fabric store has real silk of a similar shade, but lighter intensity. On my last garb project, an Aregunde robe, I used polyester for the silk when the "100% wool" I ordered online was nothing of the sort. I wasn't going to put real silk on fake wool!
(Heh. I was looking at pictures of the San Vitale mosaics yesterday, and I notice the museum reconstruction of Aregunde's veil is a red version of Theodora's lady-in-waiting's.)
Given how little I'll need if I just trim the sleeves, and since the polyester has a minimum 10-yard order, it may be cheaper to go with the real deal this time! If the color ends up being good. Maybe I'll go over there tonight and have a look.