Color chart page here (featuring slate)
http://www.mgb-stuff.org.uk/colourcodes.htm
Source: Diverse

Colour codes on the diagram
Examples :
wn = white with brown stripe
nu = brown with blue stripe
gy = green with yellow stripe
The code is base wire color first followed by the stripe color if any. Then a dash followed by "p" or "c", for either plastic or cloth outer cover material.
The color abbreviations are:
B = Black
G = Green
N = Brown
P = Purple
R = Red
S = Slate
U = Blue
W = White
Y = Yellow
Source: Tee One Topics issue # 6