Is there such thing as a sooty bay? If so, do you think Crimson is one? The first picture doesn't show his coloring real well because of the lighting but it was the only one I had. In the summer he turns bright metallic golden with black patchs starting at his neck and goes along his back to his tail. In the winter he turns a deep red and the black patches turn a charcoal grey color and extend further down his sides. His dad is a regular buckskin and his moms black. His full sister was a sooty buckskin.
Yup sooty can affect bay, as already noted. Also agreeing with P, I would say your guy is a cream dilute. I would lean towards a smokey brown though instead of buckskin, but it is only just becoming usual to differentiate between the two so P could have already deduced that too :)