The coat is the skin/fur coloration of the Krafties Creature.
When you bond a soul to a captured Krafties Creature, then it will normally change coat color based on the element (seen on each of the element and species pages). The only exception to this rule are the exotic coats.
When you catch a wild creature that has a unique coat different from their normal wild colors, it will keep that unique coloration despite what element of soul it gets bonded to.
Exotic Coat Gallery
Pictures of wild/bonded krafties with exotic coats.