Hi,

Dentalia has a dark and a light header options. You can change the header type on a page edit screen. The colors can then be set in Theme Options:

But this allows you for only two color options.

To add a third color, I think the easiest way to change the header color is with CSS. 
Each page has its own id, which can be used for setting the color. For example, Your home page id is 24618.

You can change the color like this:

.page-id-24618 .nav-container {
 background-color: blue!important;
}

if there are multiple pages, where you want to set the same color, you can write the css like this.

.page-id-24618 .nav-container,
.page-id-1234 .nav-container {
 background-color: blue!important;
}

The CSS code goes in Theme Options -> Custom CSS.

You will also need to add a transparent png logo (instead of logo with solid background), for this to work nicely. 

I hope this helps,

Andrej

Unfortunately this is not as easy. The logo is loaded through html ( not CSS ). It can't be replaced with CSS. 

The theme supports dark and light logo. If there are max two logos altogether on the site, then you can use this to your benefit, but if there are more, then it gets complicated. You would need to write a custum orion_get_logo() function. This requires moderate knowledge of php and using a child theme. The original orion_get_logo() function is located in dentalia/framework/helpers.php file. But if you create a function with the same name in your child theme, then your function will load instead of the dentalia one.

Kind regards,

Andrej