Set the colortable to use the "rigid" method of
looking up colors.
This is a very simple way of finding the correct
color. The algorithm initializes a cube with
r x g x b colors,
where every color is chosen by closest match to
the corresponding coordinate.
This format is not recommended for exact match,
but may be usable when it comes to quickly
view pictures on-screen.
It has a high init-cost and low use-cost.
The structure is initiated at first usage.