I think that the easiest solution is to change the css manually. So using your browser inspector search the div that contains the style and force it to be the color you want.
I think that the style is this one:
.ephox-polish-editor-container .ephox-chameleon-toolstrip {
background-color: yourcolor !important; // I am not sure if you will need !important
}
And if you want to change the shadow:
.ephox-polish-editor-container .ephox-chameleon-toolbar:first-child {
box-shadow: inset 0 -.5em 1em yourcolor !important; // I am not sure if you will need !important
}
You may need to change more styles probably depending of what you want to do, but I hope it may help you to understand how to change the colors.