Poop 101 
Usually a normal colour change is diet related. Does he have multi-coloured pellets? Casey goes through phases and will only eat certain pellets, right now she is on a green streak and therefore has green poop, before she was always eating the red ones and her poop was always a reddish shade. When it's more watery it's usually due to the water content of food (like eating a lot of fruit) or if they've just had a bath or if they aren't eating enough it's very watery with little poop. Normal poop is usually firm without a lot of liquid...
If you really think it's not diet related and nothing food-wise has changed, I'd give it a few days to go back to normal before getting concerned.. if you want you can use paper towel instead of newspaper to see if it's going back to normal (you can see more liquid, colour etc. with the paper towel)