It is possible to customize the color of the Book button. In your Bookeo account:
1. Go to Settings>Colors and Styles
2. in the Custom CSS section at the bottom, paste this code:
.bookeocss .gobutton .smallbLeft, .bookeocss .gobutton .smallbRight {
background: #0795fd;
}
The background-color value is an HTML color code, which you can select here: http://html-color-codes.info