Currently, if I want to allow clients to have a background fill for only a portion of the template (ex. half the page) then the only way the client can customize the colour is by using a text box. This brings its own problem of having a prompt for the client to enter text, even though it is meant only as a colour fill. If the client could be allowed to modify the fill of an image in an interactive template that would solve this issue.
This is a definite need for us. We have a new client that wants their users to be able to change the background using a color picker. The above method is the only way that I was able to achieve this. I added field scripting to the input box to prevent any text from being included in the file, but it is janky because the user sees the text in the designer window.