Mica is translucent and reflective. It is non-color uniform in it's spectra concerning this matter. Gesso is designed to be a basecoat material for painting, or making art. all colors under the sun are used with Gesso as the backdrop. Some paints -oil and acrylic- are transparent by design. No paint or coating is truly opaque. All exhibit transmission of light, including Gesso.
A simple recipe for a 100% chance of uneven color balance, which Gesso is emphatically NOT allowed to have or show.
The resultant effect when using mica in gesso , intended for making art canvases.... is to emphasize differing colors over others, and color-shifting will be evident. dull in some spectra, shifted in others, etc. No artist worth their salt would ever touch it.
Only an idiot would design Gesso with mica in it..or they where trying to save money over the use of sintered titanium source costing..which is the finest ingredient that can be used. I only know of one basecoat that uses this most expensive ingredient exclusively, for the best reflectivity and best color balance within in that reflectivity. Ie, a "no Compromise" basecoat of the highest order. Zero filler, with the reflectivity of a mirror, with better color balance than that mirror.
So, this product may have mica in it, but that's not necessarily a good thing.
So, I'm not trying to get on you about this subject, but.. it ain't a proper Gesso, if it does indeed exist.