Editing dashboard or header font and image colors

[j-ed]

I think it is called “Theming” what you are looking for. You find related information in the Admin guide and also by using the search function of this forum. Example:

Theming: Custom CSS

A very cool app to hide items such as the remember login checkbox or the contacts menu – without editing the original CSS files. Thanks @juliusknorr! https://apps.nextcloud.com/apps/theming_customcss https://github.com/juliushaertl/theming_customcss