How can I simply set the color (HSV or RGB) of a pixel in a costume?

[kinestheticlearning]

Jens, in 2019, you edited a similar project of mine and it worked, but now it doesn't work anymore. Can you look into it, please?

Here's the link
https://snap.berkeley.edu/snap/snap.html#present:Username=kinestheticlearning&ProjectName=Media_Map_Transparency_edited_by_jens