Nice macro shot, you'll enjoy the photos you can take when you use the little flower button.

The poo doesn't look exactly like salmon or trout, it's a bit more translucent than I normally see. And that you fed pinky last would imply that this poo is a feed behind what you last fed - I'm not sure the digestive transit times and whether some passes quicker. When a snake poos a few days after feeding is that the most recent feed, or do they have two or three feeds digesting at the same time?
The fact that all three of your snakes have the same colour poo would suggest that it is down to the food, providing they are all fed the same?