no header color

You’ll need to set some CSS and probably create an image with the transparency you want. Are you using a Child Theme or do you have the plugins, “Custom CSS” or “Jetpack”?

Try the Jetpack plugin as an alternative to a Child Theme for CSS changes. Jetpack has a section named Custom CSS which holds and applies your CSS modifications externally, so you don’t edit the theme’s files and compromise your changes when the theme updates.

In the Custom CSS section of the dashboard, enter this;

#branding {
 background: transparent;
}

If that doesn’t work, try this;

#branding {
 background: transparent !important;
}

It doesn’t look like your Jetpack plugin is using its Custom CSS bit.
Here’s a guide for using the Custom CSS section of Jetpack http://jetpack.me/support/custom-css/

Your webpage view-source:http://play.annenas-multimedia.nl/ (source) doesn’t have the transparent CSS in it. I don’t think that plugin is working correctly.

And Thank you for contributing to the WordPress community 🙂