1. Open your jpg, bmp, gif, etc image file using the Microsoft Paint (Programs -> Accessories -> Paint)
2. Using the “pick color” tool in the toolbar located in the left (it looks like an eye dropper), drop it or click it on any part of the image that you want to determine the RGB color value. You should see the lower-left color indicator changed to the color that you have pointed or clicked.
3. Now in the Menu Bar, go to “Colors - > Edit Colors…” and click “Define Custom Colors“. A window will pop-up showing the Red, Green, Blue (RGB) values or number, Hue, Saturation, and Lum. Note: The value is in Decimal number; some applications, like in HTML publishing, require a Hexadecimal number format. In short, you have to convert the Decimal value to Hexadecimal.