This add-on will be a little more challenging,
because this video will just get you started.
You will use your persistence and curiosity
to figure out the rest.
First, make sure the sprites in the project
can change color, black and white sprites
don't react to the Set Color Effect To block.
So, click on the Costumes tab, choose a color that isn't
a black, white, or gray, then select the Fill tool.
Now, from the Looks menu,
use the Set Color Effect To block, connected to some event
or conditional that will cause the color to change.
If you've liked one idea for how to do this,
watch the rotating add-on video, and replace the Turn block,
with a Set Color Effect To block,
or use Event blocks.
One of the great things about computer science
is there's lots of different ways to do things.
What matters most is the results.
Explore until you have something that works.
Once you've finished this add-on, update the instructions
on your project page, so users know
which keys to press for the rainbow effect.
Now it's your turn,
change the color of the stamps, so they can be affected
by the Set Color Effect To block.
Use events or conditionals and the Set Color Effect block
to make the change in color happen.