RGB and HSV

 Display devices like computers, mobile phones and so on generally use a different colour model called RGB, which stand for RED, GREEN, BLUE. One of the most difficult aspects of desktop publishing in colour is colour matching. Colour matching is properly converting the RGB colours into CMYK colours so that what gets printed looks the same as what appears on the monitor.

"RGB colours are also knwon as 'additive colour', because there are no colours and the colours are being added together to achieve further colours or until the outcome is white(look at the colour chart image directly below, the inside colour is white because it is all the colours added together). This is because our eyes receive no reflected and they perceive the colour to be black. However, when you add portions of red + green + blue the outcome is the CMYK colours.

HSV stands for hue, saturation and value, and also is also often called HSB, B being for brightness.

Hue is the colour chosen.

Saturation is the amount of white desired in your particular colour, being very washed out or very clean. It has also been described as The "colorfulness of a stimulus relative to its own brightness".

Value on the other hand is how dark or shaded you want your colour to be. 

If the user has selected as colorful as possible a dark purple  , and then shifts the lightness slider upward, what should be done: would the user prefer to see a lighter purple still as colorful as possible for the given hue and lightness  , or a lighter purple of exactly the same chroma as the original color