You can change the color or add an image of your choice to the header. To do this, open your Dashboard (top left corner), click on Settings (left side) and then Widget .
Scroll down and click on Advanced setting then scroll down to the the "Design" section.
Changing the color of the header:
In the "Widget header color" field, put the the hexadecimal code of the color you want. You can find the hexadecimal code for any color here http://www.colorpicker.com.
Here is how it looks:
Customizing some CSS
Hiding the name of the company next to the logo
You'll find below an example of the CSS code necessary to remove the company text field. Just adapt it with your image, and copy/paste it in the "CSS code to use in widget" text area. Notice how the name agendize is not displayed next to the logo anymore.
Here's how it looks:
If you know more about CSS, you can try to add other things! Feel free to customize your widget.