You should be able to buy "textile pigments" in the cultural market. Each box is packed in a small bottle. If it is not enough, you can add propylene. No, when using propylene, you can adjust this pigment and iron it with an electric iron after painting. The paint instructions say how to perm it. The color will become very bright and thick after ironing, so you must take this into account when painting.

Take a piece of waste cloth to do the experiment at the first time, so that you can take a lot of detours less.