Better than RIT dye would be Procion dyes, from your better craft
store, such as Pearl Art and Craft. You’ll have a much greater
range of colors to choose from.
There are two types – one for cotton and one for wool/silk. So you
have to determine which would work better with the MOP. The dyes
come in powder form and you mix them. The one for cotton is fiber
reactive, the one for wool/silk requires heat.