Changing image colour online

[wakecarter]

If I understand the issue correctly, this is about changing the colour behind a mask.

You could present a coloured polygon behind an image with a transparent foreground rather than using the mask feature.

Experiment involves using images as masks

Cool. However, that working locally doesn’t necessarily mean that the method will work online. I know that there have been some issues with the mask parameter so it wouldn’t surprise me. You could try replacing the image with a flat color rectangle, possibly a transparent png, but I’m out of my area of expertise here.