Hi I use a white undercoat, and try not to go over the bits I need to be white.
I do tend to use white as an undercoat for anything I use for dipping unless there is a colour spray I can use as an undercoat.
Some of the people on the Warlord forum suggest using Army Painter Leather Brown spray then the Dark tone after block painting.
Have finished my 4th base and second units of skirmishers. Now will wait until the NNC are released (or until I see the sprues) and see if there is any more variation I can get into my Zulu units.
Now have a chariot army to paint (Newline had a sale
and sucked a load of money out of my pocket) 28 chariots to do.
Thanks for the comments.