Illumination Equipment
A whole lot of things are needed in addition to what you use for calligraphy:
paint, brushes, vessels for mixing paint, a pair of compasses, technical
drawing pens etcetera. This file will give you some hints about inexpensive
stuff. It does not, however, teach such advanced things as making paint
from natural pigments, or applying gold leaf.
Paint
The simplest way to put colour on an illumination is to use felt-tip markers.
But don't! The pigments aren't good enough, and will fade or darken very
fast. I have seen a brilliant green turn to almost black in a matter of
months! DON'T use felt tip markers, especially not the water soluble kind.
Another simple way is to use crayon pens. These colours are more durable,
but they still won't do. It's almost impossible to produce an even, smooth
surface with them. The appearance of the illumination will not be authentic.
You can use crayon pens for mending little errors on almost-finished illuminations.
The only colours that are good enough are water soluble, opaque colours
which you apply with a brush. This is the type of paint, often called "gouache",
that was used in the middle ages. I use something called "Pelikan Plaka"
which comes in little glass jars. I'm not sure if you can get this in America.
It's water soluble but hardens and becomes virtually waterproof when it
dries. This paint is easy to work with and will last many years. A friend
of mine has a painting in Pelikan Plaka on his wall which is some 30 years
old and hasn't deteriorated at all.
Real gouache comes in tubes and will not become waterproof when it dries.
These paints are generally more expensive than "plaka" type paints,
and I don't know if they're any better. Some calligraphers use acrylic paints,
but I have never tried that (the word "acrylic" gives me the creeps).