How to Make Pixels ( = fuzzy equal to certain RGB values) Transparent.

Thank you, Jens.

I have noticed you have after all implemented the idea quoted above in the last version and I now think - inspired by other kids' self-confidence here Last Digit Block! - a credit to me would be a deserved one.

Sure! Why don't you tell me your name (send me a private email), and I'll be happy to do so!

A bit late to the party, but I was confused about the output of the map block in your version: for the gray pixels it would output a pixel of [[55, 55, 55, A], [55, 55, 55, A], [55, 55, 55, A], 45], i.e. a pixel where the red, green, and blue values are the entire input pixel. I was surprised this worked at all.
Media_Map_Transparency_edited_by_jens script pic

I have not been following this thread lately, so I haven't seen your reply.

But, yes, you are right - see the discussion here.