No/different looking material shown in render

Hello there,
Can anyone help me with this? I applied a basic principle shader to my model to give it a basic material. As you can see in the images, the material does not show up as expected. It does not even look coloured. At first I only noticed the brakebrackits which are supposed to have a red material, to look white in the render. I mean white, not a light red or something like that.
The Rim looked with its basic glossy material a bit wrong as well. Some areas of it looked like how they were supposed to, glossy. But the front of the rim is as well more like a white colour than a glossy material. I thought both things could have something to do with the world settings? I tried the standart world settings. They had the same effect to the material. I think so. Maybe I am just a little confused and forgot something. ? A HDR Image as world background/lighting did not help as well.

Any solutions for this? By the way. I am obviously using cycles.

Thanks for any help.