I'm not clear how the "paste on" block works. I wrote a simple test project https://snap.berkeley.edu/snap/snap.html#present:Username=s_federici&ProjectName=paste%20on and I expected the "turtle" sprite drawing a line on top of the "square" sprite. Instead the line is drawn on the stage, as usual. What am I getting wrong?
PASTE ON is like stamping, not like drawing. The sprite that invokes PASTE ON has to be on top of (or at least overlapping) the target sprite. And then a picture of this sprite appears on that sprite.
I see. Thanks. I tried PASTE ON "another sprite". The stamp shows up both on the sprite and the stage. Is this what it should do?
You say PASTE ON instead of STAMP. It should only appear on the sprite.
Oh, I see. I thought it was a switch, not an actual stamp 
So, "PASTE ON Stage" is the same as STAMP, right?
It would be cool (even if I don't know if really useful) being able to draw also on sprites. Maybe the PASTE ON block could become a "DRAW ON" switch, that allows you choose if you stamp or draw on the stage or on other sprites.
You can fake drawing by giving your sprite a dot as its costume and then
This is interesting. Even if, creating a drawing with all the desired colors wouldn't be so easy, would it?
Right, you'd have to use the color effect.
That is what I thought. Are there good starting colors and a good way of getting a reasonable amount of colors out of them, that is out of the color of one (or several) costume?
"color effect" controls hue, so, you know, start with RGB.