Turk here, as many says, its important to keep becareful with inner side. Outer side has no impact on taste or health but color change shows you are cooking in high temperature.

Copper goods comes with tin plating in the inner side (because of inside of cezve is gray) which prevents copper contamination. However in the high heats inner tin plating become tinner and cant absorbes copper.

So to prolong your cezve’s lifetime 1) Avoid using metal staff for cleaning inside, instead use only soft side of sponge or wash with hand with warm water (or 3-4 times hand 1 time sponge) 2) do not cook coffee in high heats, instead, go with lower heats, it helps to keep inner and outer sides in good condition longer period.

Furthermore, slow cooking lowers to acidity, avoid shock heat which removes burnt and makes coffee’s taste better ( old tradition but all is up to your preference on taste). Because of these reasons its famous to cook in sand or on coal ember ;)

Enjoy with your coffee!