Color white - (Color white alpha:0) = Color white
Color white - (Color white alpha:0.5) = Color gray.
Color white - (Color white alpha:1.0) = Color black.
For what do you need the color arithmetic ?
Maybe there are already other operations defined on Color that you can
used instead.
That is too complicated :)
The idea was to have one-line fix that just leaves the behaviour as it was before, simply makes it not produce garbage.
Basically there should be a long discussion after pharo 4 is released.
How it is now:
(Color white alpha: 0) = Color transparent => false
Color white - (Color white alpha: 0) = Color black => true
From logical point of view is should not be black. But from mathematical point of view Color is just a vector and operations with it should be the same or almost the same as with vectors.
For what do you need the color arithmetic ?
I wanted to get linear discrete transformation from one color to another to use it in animation��