Thanks for using Petco Pet Education Center, formerly Petcoach! It looks like Kusion broke his toenail and now the pulp of the nail is exposed. This is likely painful and he is licking it a lot causing the color change of the fur around the nail. I would take him to the vet to cut away the broken part of the nail and get him antibiotics and pain meds to prevent infection and give him comfort. You can also soak the foot in epsom salt bath until you can get to the vet. Good luck and kisses to Kusion!