[tp2357]

Something else that might help is changing the color representation from Red-Green-Blue (or Blue-Green-Red, if you're an OpenCV user) to Hue-Saturation-Value.

Thinking about it geometrically, RGB (or BGR) maps colors as a cube, with the corner on the origin being black, and the corner opposite diagonal from it being white. HSV, on the other hand, plots colors as a Cylinder. With Hue (the type of color, i.e. red, green, blue) being a value rotated around the centre of the cylinder, and saturation ranges, on has a color as it appears in all lights. If you set a wide range for the value (how light or dark the color is i.e. how close the image is to being black) you have a more light-difference representations of the colors that you're looking for. Just be sure that you convert back to your original color representation notation, or you'll run into problems there.

I hope this helps, i'd be more than willing to answer any questions you may have on top of this.