Map Color and Other Channels

Q4. Color can be best understood in terms of three separate channels: luminance, hue, and saturation. Briefly explain how does this system specify colors. (Figures can be used to help illustration.)
Q5. Explain the meaning of HSL /HSV and how does this system specify colors?
Q6. (a) What are three major problems with the common continuous rainbow colormap?
(b) Is there any way to address these three problems? Explain how.