I'd not worry. It's most likely a false alarm as Kulinarykidz points out. Our stool can contain the red/orange remains of pill casings, undigested parts of fruit skins (tomatoes, apples, and others) and seeds. They change color when bathed in the various acids and enzymes within the digestive tract.
When we're looking for flare signs with UC, we looking for blood on toilet paper when wiping, and signs of blood on the toilet water surface (obvious bright red drips or slicks across the water's surface). Usually it's not the only sign, it's usually paired with increased urgency or bms, or looser stools.
I know we tend to read our bms like fortune tellers read tea leaves, and I'd wager the odds of success are about
equal. It's great to be vigilant and look for changes, but inversely small changes can make us panic and worry. If non-uc-folks ever cared to look before flushing then they'd see what you saw. It's perfectly normal