Black: Grounds,
grounded elements,
and returns 
Brown: Heaters, or
filaments, off ground

Red: Power supply
B+ 
Orange: Screen
grids 
Yellow: Cathodes 
Green: Control
grids, diode plates 
Blue: Plates 
Violet: Power
supply minus leads 
Gray: Ac power line
leads 
White: Bias supply 

The advantages of
standard color
coding allow you to
quickly trace
circuits for
troubleshooting -
even one's that you
made yourself if you
memory is as bad as
mine. You heater is
coded for B+ and
cathodes which
would initially
confuse the dickens
out of me.