No, it's fine. I don't have any experience with a level editor other than the one I made for my Megaman EX game (which doesn't use a raster, it just takes coordinate positions from an origin point, and translate it into a string and save that) so I don't really know how it works. I was just making a suggestion.

These are all just my opinions. I'm kind of surprised actually at the fact that N-Game was just acknowledged on greenfoot. Seriously, it made me very excited!

Maybe change the rotate button into two buttons (rotate left/rotate right) and make them a/d, with the color change buttons being w/s. This is just my opinion for controls though.

Also, It would be better to break up the grid into quarter blocks so I could place the half-ramp on the top half of a grid space to make a y=1/2x ramp.