Soda is most definitely a dun.
He has very obvious leg barring, zippers, dorsal stripe, wither markings, mask, ear tips, dorsal extending into tail, etc.
I was thinking of testing him for cream just for the heck of it. His sire is a dun and his mother is a palamino (why I was thinking about testing for cream). He isn't particularly light but I've heard that cream can be masked very easily and I am a little curious. I should've clarified that I wouldn't be testing for dun, but cream. Sorry