With tiny hatchlings it's even possible he's pooped and you haven't found it. Also, light colored babies tend to be translucent (yes, don't worry), so you could also look through him and see if there's something before the vent if you want to make sure. I know it sounds gross, but can help you when in doubt until your little one is more established and you know his routines better.
Very nice baby, love his pattern.