One of my geldings has a big blaze and pink skin on his nose, and my mare is a medicine hat paint. I've also had other horses prone to sunburn in the past, and I can honestly say that human sunscreen isn't the best choice for horses.
I've dealt with skin cancer in two different Appies in my lesson string, and when the vet was working on the first one, he told me that human sunscreen usually isn't mild enough on a horse's skin - the chemicals in human sunscreen can cause skin irritation), and it can be ineffective because it's likely to rub/sweat off. If you're going to use human sunscreen on a small area, like a snip on the horse's nose, then using pure titanium oxide cream is more safe and effective (that's the stuff that lifeguards in movies and TV wear on their noses - a thick white cream).
If you don't want to use the titanium oxide, I highly recommend My Pony Sunblock, which is an all-natural powdered mineral sunscreen just for horses and other animals. I've been using it for a few years now - a little goes a long way, and so long as you can see the powder on your horse, it's working. Because it's only got minerals, and not any petroleum or other oild-based chemicals, it is very gentle on skin, and the powder coats the hair and bonds to the skin creating a barrier against sun and even wind-burn/chapping.
I also use Suncoat Spray by Health Hair Care. It's a spray on sunscreen for horses, and it can prevent coat fading in bays, blacks, and chestnuts as well as protecting light-colored/skinned horses.
"Quick fixes, by their nature, fix nothing; that's why they're repetitive."
"It's better to ride even if you get thrown, then to wind up just wishing you had."
- Chris LeDoux