You may be best served to get a second opinion, preferably by a doctor who will provide you with some insight beyond " your colon walls are black and inconveniencing the search for polyps ".
Also, I suspect that the Schulze intestinal formula is not the only substance you have swallowed the last several year, so you might try to diagnose from this perspective, which underscores the need for a second opinion that provides some expert medical insight.
I too have been taking IF#1 daily for several years. Regularity is much improved but have no recent 'scope work to indicate color of my colon's interior. Infrequently I also use Schulze IF#2, it is greyish black powder but also contains some brown seeds. Ive broken open IF#1 capsules before and saw they contain medium brown powder. Good luck.