Please add a green set to my order (total should be 1 black, 1 blue, 1 red, and 1 green).
If some of them don't make MOQ or people back out, I think you should consider a "tax" to bring the order up to 400. Say 380 people want black, add 20 orders to make 400 which is $180. Each person would only owe 180/380 = ~$0.48 extra to meet the minimum. I'd much rather pay an extra 50 cents than not get a full set of caps. Just something to think about. The extra sets could be sold and the proceeds donated to geekhack.