When painting on fabric - choose the textile colours for the fabric you want to use correctly. No silk colours for balloon/parachute silk ;o). For a good flag, i recommend using silk. Great to paint on. Dont know if they are sold in the USA as silk colours, the firm is "Seidicolor". Waco Fin is great too for that job.
And in case of need, i guess you will get a book like this one in every bookshop around:
http://www.amazon.com/dp/0855328029/