1. The email received after registering, has no standard formatting.
f.e. :: the separation of the greeting, the link to confirm account ... etc.
Nor is the email html.

Where is this setting changed, or where is the file that needs to be altered

It should have spacing between content just fine. Did you turn on HTML registration emails within CB > Configuration > Registration and not change the email to have HTML? It will not automatically convert the default non-HTML email to HTML; you need to supply that yourself. You can either use the parameters directly available in CB > Configuration > Registration to change the Welcome and Pending emails or use language overrides shown below to override their language strings.

www.joomlapolis.com/blog/kyle/18701-language-overrides-have-arrived

2. How do i change the color of the tabs of the profile. I have attempted template css overrides, but that did not work.

You will have to write all the necessary CSS for that. We do not provide coding assistance so I cannot help you with that. If your CSS isn't working then your selectors in your CSS are properly not strong enough to override the existing styling. We use Bootstrap 4 so all the coloring applied is provided by Bootstrap. You can use CSS overrides shown below to add custom CSS to CB.

www.joomlapolis.com/blog/kyle/18711-template-css-overrides-made-easy

Your screenshot is not of the Welcome email. That's the Pending email. You added HTML to the Welcome email, but the Pending is still using the non-HTML language string. If you're confirmed or approval enabled the user is sent the Pending email. After they confirm and are approved they are then sent the Welcome email.