Good call on dyeing the cotton balls! This could be done with a regular fabric dye, but then you would need to follow it up with a mordant, such as rust water (iron oxide dissolved in water will 'set' the dye, but it will also darken the cotton material. Using iron water as a dye and a mordant will color the cotton a steely gray color, which will not wash out for a l-o-n-g time afterwards.
Wife is into fiber arts (knitting weaving, dyeing yarn), so we took a class, together, or dyeing wool and other fiber materials. Fascinating class, learned a great deal, more than I ever knew before,about it.
Nice thing about using acrylic paints, is that they do NOT require a mordant to set their color in the material. Really nice idea.
This makes me wonder if I could use black and/or gray craft paint baths to color pillow stuffing material for battlefield smoke markers? The fibers in the pillow stuffing are man-made fibers, so they likely will require a brute-force synthetic dye, or acrylic paint, to set a color in them.
I could start with a full gray soaking color, to remove all, or most, of the white in the stuffing material, then dunk/dye small portions, in black, to vary the color saturation throughout the fiber ball of "smoke." I may also experiment with using yellow and/or red paint baths to create "hot spots" within the smoke balls, maybe doing a little tie-dyeing on different parts?…
I used to spray pillow stuffing fibers with black spray paint, which created mottled grays in it. It worked very well, but dyeing it in acrylic paint might work better. Need to experiment with some pillow fill/stuffing fibers… Thanks, Bill! Cheers!