How do I keep red rice colour when milling without the buyer rejecting it?

The red colour of red rice is in the bran layer, so the more you polish, the more red you remove and the paler and less valuable it becomes for the health market. Buyers want red rice with the bran largely intact, sold as brown or unpolished or lightly polished, so you must mill gently and only de husk and minimally polish rather than running it like white rice on a normal mill. Tell your miller to reduce the polishing passes, or use a mill that can handle unpolished rice, because a standard high polish setting strips the colour and the nutrition that buyers pay for. The trade off is that less polished rice cooks differently and has a shorter shelf life than white rice, so dry and store it well. Test a small batch at different polish levels and show the buyer to agree the right milling before doing the whole lot.