Pointillism is a style of painting which can produce some very interesting results by blending just a few primary colours. When creating paintings like this manually it can take an inordinate amount of time as each dot is individually placed. However, mtPaint is able to create these images quickly and easily with a large amount of control over how the colours and dots are chosen.
Here is a photograph:
By using the "Convert To Indexed" tool in the Image menu I created this:
I used 8 colours, Use current palette and Floyd-Steinberg options. I changed the default settings to use Separate/Split error propagation with a propagation value of 90.
To see the above images in all their glory you will need to click them to view them at 100%. As you can see from the results, although only 8 colours have been used, mtPaint has been able to blend the coloured pixels well enough to capture the essence of the original colours.
A related technique is stippling, where only 2 shades are used. This is most commonly done with a black ink pen on a white page. This can be done in mtPaint as you can see from this image:
I achieved this by loading the original JPEG, moving the white palette colour 7 to position 1 (hold the shift key, left click the white colour 7, and drag it to position 1 and then release the left mouse button), and then doing the same steps as above, but having only 2 colours in the final image.
To learn more about the specific options in the "Convert To Indexed" window, see section 6.8 of the mtPaint handbook.