1-Please make sure your logo is in proportion with the supported dimensions. The closer to the online demo (164x50px), the better.
2-You can change background color (and other styling settings) in Specular > Header options > Styling Options > Background.
3-If you set ‘Responsive Layout > ON’ in General Options, the site will be responsive. So the logo and every other element will shrink to fit all screen sizes. But is not possible to have different images for different device screen.
