Yes Bill - I used to have a Unicolor filter wheel with the red, blue and green filters for additive printing, but the filters decayed long ago. I suppose it might be worth replacing them. But I find it easier to make adjustments with subtractive filters.

I'm still intrigued to find out what happens if I mount say a 3-1/2in filter on a 6in card and use the filter drawer. I'm willing to bet it will be just fine at least for 35mm and maybe medium format.