From an artistic point of view, dot filtering can be summed up as putting down washes or glazes of various colours. The only difference is this method allows you to do many shades all at once. You can throw on what ever you want, even pinks and purples.
When you understand the properties of the colour wheel, mixing any shades from the primary colours (red, blue and yellow) you will arrive at a non colour which is essentially black. Since the dot method involves some sort of thinner to dilute and mix the colours on the surface, you will end up with greys that have a slight shade to them depending on which primary colour was more dominant in that particular "streaked" area. Of course the background colour of the build subject will also effect this.
regards,
Jack