The color of the board shows the composition of it, hence the use of it.

Original and older boards were bakelite composition, and were brown.
Phenolic (spelling) was a tan
Most "non filled" fiberglass boards used in computers are green.
Filled fiberglass is blue.
Teflon is white.

As boards evolved more and more demands were made of them.  First boards were
used mainly in audio circuitry.  Couldn't be used in high voltage or RF because
it would arc and burn.  Most boards today are fiberglass, the type being chosen
by its use and cost.  

Boards in satellite and microwave communication are teflon (and ceramic) as the
fiberglass, and other boards are conductive (they actually work more as a 
capacitive dialectric, but the word conductive simplifies explaination) at the
high frequencies.

Another printed circuit material used mainly in automotive and interconnections
is a thin flexible (mostly mylar) material and is used to connect the front of
the vehicle (etc) to the back instead of wiring harnesses.  Camcorders use this
to intereconnect the boards inside where wires would be a nuisance.

Am working on a generator made by Hewlet Packard right now and the entire board
is gold plated, boy it looks expensive!!!

Hope I got most of my facts right as I am working from memory of material read.

My education was pre-transister!
-- 
73, Tom
================================================================================
Tom Wagner, Audio Visual Technician.  Malaspina College Nanaimo British Columbia
(604)753-3245, Loc 2230  Fax:755-8742  Callsign:VE7GDA Weapon:.45 Kentucky Rifle
Snail mail to:  Site Q4, C2.   RR#4, Nanaimo, British Columbia, Canada, V9R 5X9  