I found the problem
This is the new link to the project
https://playcanvas.com/project/482459/overview/moonexperiment
http://academic.cast-soft.com/3dlandingpage99/index.html
It seems that the color is coming from the camera “clearColor”
Now it’s fully transparent, yay!!!
Note: I think there is some sort of problem with this control, I setup it first with a solid pink color to debug. When I came back I put the 0 on the alpha channel, but didn’t touch the other channels, I had a semi transparent background. After that I put everything 0 but there was still a hint of blue, I checked again and something changed my setting in the blue channel (maybe when I clicked outside to close the dialog). It only became fully transparent when I put everything 0 0 0 0 . So I think there are two bugs there, one related to the input that changes when you close the dialog and another related to the alpha channel which only works if you put all 0.