Pale discolored poop chunk?

Hey everyone. I’ve had IBS forever. Lately I’ve had the floating fatty poop and things seemed to calm down. I have been having some colon pain for the past few months, but I believe I have gluten sensitivity or celiac. I’m seeing a gastro in 12 days about that.

My concern was that I pooped today and it was the usual mucus IBS-D poop but a quarter of one of the chunks was white. Any idea what that means?