Uploaded image not showing in Firefox Color custom theme

I created a theme in Firefox Color but the image that it shows in the preview will not populate in my actual browser toolbar / tab bar, it’s just the colour settings I chose. It is well under 1MB. Am I missing something?

did you set transparency on the color?

I don’t see a place to do that, where in the settings is that option?

How do I change the toolbar color from being transparent to being white? I want change this for https://yesornogenerator.com/