Add this code to your additional.css template to match the colors of the editor to the style you are using:

/* Background Color for CKEditor */
.cke_skin_kama .cke_wrapper {
background:{vb:stylevar postbithead_background} !important;
}

/* Background Color for CKEditor Buttons (Note, this may be too dark for some styles. If so you can delete this one.) */
.cke_skin_kama .cke_toolgroup {
background: {vb:stylevar postbit_foot_background} !important;
}


/* Background Color for CKEditor Hover Link*/
.cke_skin_kama a:hover {
background: {vb:stylevar control_content_hover_background} !important;
}

The additional.css template can be found here:

Admin CP -> Style Manager -> Edit Templates -> CSS Templates -> additional.css




Note: If you want to change these to your own custom colors, then use this code instead:

/* Background Color for CKEditor */
.cke_skin_kama .cke_wrapper {
background-color: #xxxxxx !important;

}

/* Background Color for CKEditor Buttons */
.cke_skin_kama .cke_toolgroup {
background-color: #xxxxx
x !important;
}

/* Background Color for CKEditor Hover Link*/
.cke_skin_kama a:hover {
background-color: #xxxxxx !important;
}

...with xxxxxx being the hexcode of the color you wish to use.