I first encountered the idea that thin "stains" of watered down paint over a white undercoat could give an impressive result with little investment of time in rules box for the RPG Traveller: The New Era.
The recommended approach was to apply "stains" of thinned-down paint over a white undercoat before finishing with a brown wash to outline the details. A stain is diluted paint but not as diluted as a wash.
As it happens, when I bought the rules in 1993, I tried out the approach using some actual Traveller miniatures - 15mm Aslan from the original GW/Martian Metals range.
They are a bit worn as they've been in storage for 26 years but I think you can see that the stain gives highlight and shadow to cloth and fur particularly well.
This civilian is a Traveller figure too...
As are these guys in vacc suits...
I've not really stuck with the technique for whole figures, though it is quite quick to use, but I do use it for parts of figures from time to time. An exception is this recent spirit, which uses an all-over stain technique.
So my advice is buy GW Contrast Paints if you like but bear in mind you may get just as good an effect with conventional acrylics and water.