ActorPositionWS can I control the range of different colour outputs?

Hi I came across the ActorPositionWS vector and the example I found on unreals web page.
link text
Seems like a cool thing when having multiple instances of a prop in a scene, since the position of each prop causes the actor to change its colour.
My question is:
Is there any way to control the range of colours from this?
For example I have a Box with a brown texture on it, and I would only like it to change to brown yellow or darker brown or lighter brown (not blue or red) each time I move the box around in my scene.
How would I go about doing this?
Thanks in advance