Always keep an RGB copy of your original before converting to Indexed color. The reason should be obvious - most of the image information is lost forever as soon as you convert it, and you can't get it back by changing to RGB again. HSV HSV color stands for Hue, Saturation and Value. As in the rainbow, the starting and ending color is red. Hue can be described as a color circle with red at 0 degrees, yellow at 60 degrees clockwise, continuing with green, cyan, blue, magenta and red again at 360 degrees.
Value is all about brightness.
Zero for Value means totally black, and 100 is the brightest Value a color can have. The HSV color model is used in the Image Dialog for Map, Adjust and Channel Ops. It is also used in certain filters and Modes. NCS NCS, or the Natural Color System, is the system used by architects and interior decorators. This is also the system they use at the chemist's when you buy paint for your house etc.