Go to Design page.
Select “Inherit from theme colors” button in the Pre-order button style section.
Click OK on the pop-up.
If you have Pop-up blocker turned on, please allow the pop-up for this site. It is necessary to read button styles and update preview.
IMPORTANT NOTE: If you publish a new shop theme then pre-order button styles remain from the previous theme. Please follow the instructions on how to update here. If you have any problems, then you should contact support.
You can do so by going to the Design page
Updated over a week ago