I'e had very good luck brush painting light colors (whites, greys, greens, blues etc) by thinning them with laquer thinner. I usually brush MM and Humbrol enamels and the laquer thinner seems to make the paints flow together better behind the brush than enamels thinned with enamel reducer. When I open a new bottle of paint that I am going to brush on, I add three or four drops of laquer thinner and that seems to work very well.