I assume this is for artists so sure thing
I imagine that this dog is very tall and sleek (like a good five feet tall), with a sickly pale (with just a hint of light blue hue). Its eyes are a pure empty (yet still piercing somehow) white. Along its front half across the back and its legs are pale green sets of stripes, almost like racing stripes.
As for how the ghostly “back legs” worked, they looked sort of like this
with his physical form slowly transitioning into an pale blue ectoplasm, and there were amorphous hints of what could have possibly once been legs. Despite completely missing his back half, the posture seen here is still its regular posture, standing straight up, as if a soldier at attention.