I will talk about the use of colour and the theory behind it as a reflection of my practical project; technical wizardry. This post contains my working methodology and some digital painting technique that I discovered.
Brightness
Brightness is one of the most important elements that define the composition in a piece of drawing, the object’s layout, light&shadow and the geometry relationship. So we often start a painting from a grayscale sketch. this technique is called Grisaille, has been widespread in the 19th century.
In my case, I also recommend using this method as the start of the painting. AS in the early stage, the most important things is to get the composition and the relationship between light&dark correctly.

In this painting, I have placed the character in a backlight position.
Colour constancy & environmental light
To make your painting interesting, you need to learn how to dealing with the colour constancy. Everybody has the common sense of “The sky is blue, the roses are red”, and this stereotype is the main cause of the boring colour combinations. To solve this problem, the only ways is to observe the natural world, an example: the skylight is the main factor that affects the colour that you observe, but you might not notice that during early morning the skylight (sunlight) is yellow, during the daytime is blue, and in the evening is red/orange.
Thanks for modern technology, we don’t have to work out what colour that you see is under which type of skylight (think about the Gold or Blue Dress Quiz, it can be very confusing).
Adobe Photoshop can complete the process for us, just by adding one layer of “skylight” colour with the [multiply] blend mode. (layer>layer style>blending option)

Colour Wheel and HSB colour system
The colour wheel has been first introduced by Issac Newton in his book “Opticks” in 1704, he rolled the spectrum around in a circle, to make the relationship between each colour more straightforward. Base on this colour theory, people have invented many different colour systems (e.g. Lab, RBG, CMYK) but I like the HSB system the most.


Give a better example in actual software:

For some recommend drawing technique on drawing highlight and shadow by using this colour system:
- Always adjust the Hue value a little bit, rather than only adjusting the Brightness value to create the light and shadow effect.
you can see the difference between only adjusting the Brightness value and adjusting both B and H value.




I have done two drawings using the above methods for the same character, I hope you can feel the difference.

(Only adjust the brightness value)

(Adjust the hue and brightness value)
Reference:
[1]Newton, I., 1730. Opticks:: Or, A Treatise of the Reflections, Refractions, Inflections and Colours of Light. 1st ed. Oxford University: William Innys at the West-End of St. Paul’s.,