Looks pretty normal I just wanted to make sure it wasn't neon green which can mean sickness.
Yep they drink lots of water so most of their poop is going to be watery and the color of what ever they have eaten. Make sure the lettuce and peas is snack and starter is main feed. might want to add some form of niacin to their diet also since your using chick starter water fowl babies need more niacin that chick starter can provide. Would love to see your babies when you get a chance I sure do love my Runners.
Niacin supplements
Nutritional yeast 1 tab per cup of feed till 10 weeks old
B Complex liquid 1 Tab daily mixed into peas or dried meal worms
Brewers yeast 1 Tab per cup of feed
Plain niacin [not time released or flush free] Mixed into water and given daily 125 mgs per gallon of water.