If you post a pic from behind we'd be able to tell you for sure, but I'm betting it's countershading, that would be why it's so light. When they are dun, they are born w/ a dorsal and other dun factor, it doesn't come and go (although alot of foal colors can be deceiving because alot 'appear' to have dun factor that actually don't).
I'd say Soda is also a dun, but again seeing a pic from behind and we could tell you for sure. What color are his parents? Depending on what they are if I was going to test I'd test for cream, see if he's light dun or buckskin dun (from the few photos I'd be leaning towards light dun).