[n4r9]

One of the linked studies has the following (emphasis mine):

> Server race has also been shown to affect tipping. Black cab drivers receive smaller tips on average than do white cab drivers ... This is true regardless of the race of the tipper – both black and white tippers give white drivers larger tips than black drivers

https://static.secure.website/wscfus/5261551/uploads/Busines... (p19)

That's about cab drivers but I don't see why the case would be very different in restaurants.