Hi Laurent,
About logo
If you install quickstart you will see only one, main logo (3), the first one (1) is only on our demo.
You can change site logo in any template using the same steps: Template Options > Basic > Logo > upload & choose > Save . You can use logo (png, jpg or svg).
About color of burger menu
Simple Custom CSS is needed, example:
#modal-menu-toggler, .logo-image svg #primary {
background: yellow; }
Unfold is based on Helix template, that's why general Documentation is also for it. https://www.joomshaper.com/documentation/helix-framework