Color change of case

[Kbatu]

Hello Tom's Hardware community. I have a Samsung NP300E3C model laptop. I decided to clean the dust inside the of my laptop. I opened the case and I saw that the bottom part which comes off has changed color from black to bronze with rainbowish endings(1. picture). The only piece which has the same color is shown in the 2. picture. Its the piece with the upside down U shape. My question is whats that piece and why did it changed color and the color of the case?
1: http/i.imgur.com/TJksk5L.jpg
2: http/i.imgur.com/5pjzFWl.jpg

Thank you for your time.

 

[Someone Somewhere]

1) Copper covering, for radio interference protection. It's painted over on bits you might see.

2) Heat pipe. Conducts heat from the CPU to the heatsink, which the fan blows through. Outer layer is copper, because copper conducts heat well.

 

[Kbatu]

So is it normal that there are rainbowish parts on it but not the whole copper?
EDIT: I mean the piece on 2. picture the metal piece looks like it changed color.

 

[Someone Somewhere]

That rainbowish colour is a very very thin layer of copper. It does cover the whole thing, but it's not extremely evenly applied.

The black bits around ports and edges are where the black paint from the other side covers the copper.

 

[Kbatu]

Alright, thank you for your help. Have a nice day.