The easiest thing for me to do is tap into the wires in the ceiling
fan... however, I have no idea which ones I should access.
The colors a
Black
White
Red
Green
Blue

Which ones should I add the external light to? or is this a really bad
idea?

The black and red wires coming out the box (not part of the ceiling fan) are
probably the hot wires from each of the two switches. The white (coming out
of the box) is the neutral, and somewhere up there should be a bare copper
or green ground.

If the red/black pair control the fan/light, you can probe them or unhook
one at a time to see which one comes from the light switch. Or, look in the
switch box and see if you can deduce which color controls the light. Then
you run your romex (the household wiring) from the new light into the box
above the ceiling fan and connect the white to the other whites (neutral)
and bare copper to the ground. Then connect the black to the appropriate
wire, either black or red and it should work.