Paint Shop Pro can do that (and I'm assuming Photoshop can too). You bring up the graphic and use the dropper tool to select the appropriate color from the graphic. In PSP, you then double click on the color swatch and it will bring up the color palatte. On the bottom, there is a block which has the HTML# for the color you've started with. You may need to be in 16 million color, but I'm not sure......
If this doesn't make sense, please let me know and I'll try to explain better.