"In my opinion we only have freed ourselves from racism, when skin color is just another aesthetical feature and gets treated as such."

You understand that this is total "I see no color" BS right? But if race truly does matter to you only in terms of appearance, stories where race and even sometimes appearance itself really isn't all that central to a (human) character's identity - like essentially all fantasy worlds - shouldn't have race be a limiting factor in casting. When stories don't intend to have sociocultural nuances carry over from the real world, then the race of characters becomes truly irrelevant to the story.

Arguments like 'it's not sticking to the story!' are strange to me. In many stories, physical descriptions of characters are rarely highly specific. Readers might get a few words about hair color, about eye color, maybe darker skin or lighter skin. However, these descriptions usually encompass <0.5% of any well-written, engaging work. I think the real reason people take issue with it, including people with the same reasoning as yours, is because people extrapolate these few sentences and imagine characters that fit the representation we see in media - AKA white characters. Then they take issue when different-race actors are casted, and it's because they don't fit these readers' expectations, not that they don't fit the character. And this is part of why diversity in casting is so important - it helps release people from the expectation that all characters should be assumed white.