Color
If using red you can use the nearby colors almost however you want, colors that are let’s say 25% away
on the color wheel can be used up to 75% saturation, if 50% away then 50% saturation if on the
opposite end of color wheel then you can only use 25% saturation.
Why? Because let’s say you have an aquatic scene so it’s lake blue colour, if you use a bright saturated
red it will be an eye sore. In other words colors react to one another, and they don’t exist in a vacuum.
While you certainly can use red in that situation, most of the time you will get the desired effect with
less that 25% saturation. Of course this is not a hard rule, but just a way to keep track of the general
image.