Not many yellow shirt sold so far. people want to stay discreet.
My bet is on an orange T-shirt soon, if both side mix and buy it, jackpot.
Another choice could be a reversible T-shirt, red in, yellow out, use it inside out on some occasions...
Those manifestations look like a benefit to the Thai economy, stuff and food is sold in mass.
Few years ago a foundry guy made a fortune with a revival of the amulet trend.