Question about brake rotors?

[POW]

Hi guys
Just got my rear rotors and pads replaced.all fine but after I wash my car I notice there is some rust stain on the metal part between the disc and the wheels, don't know what the actual term for that part is and hope you know what I'm
Talking about. Does it matter?I understand it is ok to have bit of water rust after wash on the disc n will come off when I drive it, just not sure about this "neck" bit?
And it doesn't look good either,it is in silver colour same as the disc bit , can I do something about it.or how can I clean them without removingthe wheels?
Thanks for your help

[Valver.]

That's called the rotor hat, and no, the rust isn't an issue whatsoever

[noone]

I believe the rust is mainly from the brake pad material, as it is fine, builds up quickly.

[POW]

Thanks guys
Good to learn something about cars. Good that is not an issue but is there any ways to avoid them or clean them as they look ugly to me
Thanks