Milhouse or Millhouse, never know one L or two. I actually think you made them very recognizable, but it is best to do the line art on one layer and the coloring on the layer under the lineart one. That makes it possible to not get those mean white spots. :D. Use the bucket/fill tool only if it is for large parts (like the background) or if you are willing to mega-zoom in to fill the white bits. Believe me, it is much easier to use layers.