I have been a professional photographer fpr over 25 years and I have photographed hundreds of paintings. Oil paintings, watercolors, etc. Your flash is washing out the colors because of the angle you are using. Anyway, you are better off with hot lights and umbrellas which will give you a softer, more even lighter, but a little less contrast. I use two lowel tota-lights with FDN, 500 watt lamps, each on a light stand with a 30 inch umbrella. Place each light at a 45 degree angle to the painting and adjust for even coverage. B&H in New York city has a good selection of lighting equipment. Also, Calumet, Lens and Repro and many others. Tell me where you live and which camera you are using and I can advise you better