I have had some good results with a toothbrush & a small stiff shoe brush when doing splatter finish. I always use acrylic paint; you can get it in lots of colours in 99p pots from any craft type shop, B&Q etc. Always start with a light background colour, then apply the speckled colours one at a time as required. Once you are happy with the finish, give it a coat or two of clear spray acrylic.
Acrylic paint is easier to clean up afterwards, and it is faster drying, and you can also use latex gloves to keep your hands clean.
Check out the photos: