Comparison photos are hard to set up, especially with less common colors and patterns, but sometimes you just get lucky. These two horses were performing at BreyerFest and their owner was kind enough to set them up so I could get some shots. The horse in the foreground is an overo with a predominantly white face, while the horse behind him is a cremello. As this photo shows, while cremellos (and perlinos) are pink-skinned, unlike the pink skin under a marking, there is a small amount of pigment. That is what gives the skin of the cremello in the photo a slightly dusky appearance compared to the true pink skin on the overo, and also why he has developed freckles.
That small difference in pigment was used when breeders were campaigning to overturn the ban on cremello and perlino Quarter Horses. The argument was that the horses could not be albinos (and therefor defective) because they did produce pigment, albeit in small amounts.
It also causes a certain amount of confusion when identifying champagnes, palominos and cremellos. That is because homozygous creams can be freckled, especially when exposed to the sun for prolonged periods, and some palominos have mottled skin. An older article by Carolyn Shephard, Champagne Delusions, explains the differences between the three types of skin very well. (The link opens a .doc file, by the way.)