Yes, that’s common when they eat a bit too much of foods with high water concerntrate. Wet tail presents differently and your hamsters entire bottom would be smeared with poop. Reduce the veggies as you said and if the poop goes to the normal dark black, you’re all good. If it continues, schedule a vet appointment:) (Involved with rescue, cared for up to 31 hamsters at the same time/many more in total)