I'll tell you right now-- this is an industry wide problem-- not confined to any one manufacturer. The problem is due to the amber color of the epoxy matrix. It tends to give white epoxy grout a yellowish hue that can become more pronounced with time.

Thanks, Bill. I'm not too concerned about a yellowish hue, as my grout lines are thin, and my back-up color choices were tan shades. What I don't want though, is uneven yellowing, depending on where sunlight hits the tile (I am thinking of installing a sun tunnel).

I used white epoxy grout in my bathroom with white carrara marble. What a mistake! What I wasn't told, and found out later on my own, is that white epoxy grout and adhesives will turn yellow if exposed to UV light. So if you have a bathroom or kitchen with windows, avoid at all costs using epoxy grouts. Now, I am going to install marble countertops in my bright sunlit kitchen and I do not want the fabricator to use epoxy adhesive for the seams. The manufacturer of the stone adhesives, Tenax, has just come out with an answer to the problem and has developed an epoxy adhesive that is guaranteed not to yellow for at least 15 years. It is called Glaxs.