How do I change the color of my debossed or deluxe book cover after I have selected the initial choice of color?

You can change the cover color of your photobook from the project itself by clicking the Settings button on the side and select your choice of cover colour from the drop-down menu accordingly : 

In this sample, the default cover color selected was Leather Lavender :

Assuming you needed to change cover color to Leather French Vanilla, click on the drop-down menu and select the desired color :

Then, click the Apply button :

A pop-up box confirming your cover color changes. Proceed to click Yes, go ahead :

The cover color in your project will now show your new desired color in Leather French Vanilla: