ELSE doesn't seem to be working at the moment, I'll take a look in the next build - if it was working, it would solve your problem though
The reason it has no effect is because events are read in top-to-bottom order. When you click a sprite, event 5 is run:
Is 'color' 0? Yes it is, so set it to 1.
Event 6 is then run:
Is 'color' 1? Yes it is - event 5 just set it to 1 - so the actions run, and it gets set back to 0.
So the event sets it to 1 then immediately sets it back to 0. If ELSE worked, you'd just make the second condition ELSE.
In this case, the simplest way to toggle between 0 and 1 is to use:
On left clicked Sprite
> Set 'color' to 1 - 'color'
1 - 0 is 1 and 1 - 1 is 0 so it toggles it between 0 and 1 without any subevents.