With the recent change to add brown pigment for linen clothing, spell research's Brown Ink should probably be made from Brown Pigment + Flax Oil, like the other inks.
Currently
Brown pigment = red pigment + green pigment (General) (Use in linen clothes)
Brown Ink = orange pigment + blue pigment + Flax Oil (Alchemy)(Used in spell research)
this might be due to how color mixtures work in pigments vs light color (?) but I think it might be confusing to many people :p
Not a big deal since they can just look at the recipe book and realize the difference in the recipes.