I've been or seen people denied entry to bars/restaurants/stores based on their skin color, but it's very rare and that's about as bad as it gets. It's not like Japan where you can't go into a sauna if you've got a tattoo.
what is the explanation of not allowing tattooed people in a sauna
Tattoos are associated with Yakuza.
Is there still a taboo towards tattoos on people obviously not associated with Yakuza, like tattooed foreigners?
It's more of a dress code thing or they just dont want to serve foreigner. Not necessarily because they are racist but due to language barrier they dont want to stress about it.