A: Colour theory
Colours are described in terms of:-
Hue – the actual local colour ie: an orange leaf
Value or tone – the lightness or darkness of the hue
Intensity – how dull or bright the hue is
Temperature – whether the hue is situated on the cool or the warm side of the colour wheel and where it is within that side of the colour wheel
It is necessary to get contrast in one or more of these elements to make a colour appear brighter. I painted four “orange” leaves to illustrate this.
For the purpose of this exercise I am using the three primary colours from my palette. I mixed an orange using Winsor Yellow and Permanent Rose. If you have different colours in your palette use the warmest, purest red you have with the warmest, purest, yellow to make the brightest orange.
I mixed a wash of blue next, in this case Winsor Blue (Green shade), in my palette. Testing the strength on a scrap of paper to make sure it was as close in tone (value) to the orange leaves I'd already painted. I used this to paint around one of the leaves. This illustrates contrast in hue.