So why was his skin colour completely different at the end compared to the start cover

I know right? I was so bothered by that too. Idk why they keep whitewash black/dark skinned people all the time.

maybe is the image? because everything looks more bright? even the lines were darker in the first cap, I don't know but maybe can be it

It's the images, the first 3 chapters were done by Galaxy BL. The rest was done by someone who sniped the title and used inferior scans.