Some danes are prone to a foot fungus, very similar to Athlete's Foot. My dane has some immune problems, starting with demodex as a pup, then developing autoimmune thyroid disease, a few allergies, and fungal infections on his feet. i took a few pictures:
Here's some pictures i took of Sham's foot fungus. The first one is of the really bad foot. He has a birth defect on this foot, so it probably looks a little weird (the two middle toes were amputated at the tips and don't have nails anymore). The primarily effected nail is on the right in the picture. i'm pressing on his pad so that the nail sticks out from the bed as much as possible so you can see the fungus. This is the fungus growing on a white nail:
You can see where there's reddish brown stuff at the tip of the nail, and again at the base. When the fungus starts to die, it turns browner and starts to flake off (that's why there's a blank spot in the middle of the nail).
This is his front foot, with a better picture of what the fungus looks like on a black-colored nail. It's a little harder to see, but the redness at the base and the off-coloration are clearly visible. i was again pressing on the pad so that the nail stuck out as much as possible. On the white nail, i wasn't pressing, so you can barely see the redness at the base of the nail. If it's not a bad case like Shamrock's, you might have to look pretty hard. All 4 nails on this foot are effected :(.
If you suspect your dog has a fungus (they will probably lick their feet or other infected areas a lot, and you'll see redness like this), take the dog to the vet. They'll probably prescribe a medication similar to over-the-counter meds like Athlete's Foot meds. You can use OTC meds, but because they usually come in spray form (and dogs hate sprays generally) or powder form (which doesn't stay where it belongs on a dog), i definitely prefer the prescription Micazole lotion (liquid form) that the vet gives us. One bottle costs about $14 and lasts a few months, so while it isn't cheap, it will help your dog feel better. You'll probably have to continue to use it daily for as long as a year.