Many of the dark woods we use for guitar-making have light-coloured sapwood which is usually lost in the cutting process. It seems also more prone to fungus or insect attacks so it can have holes or a spalted figure. In any case it can make for a dramatic look in a finished instrument and if it is relatively healthy we like to use it. This is the most typical configuration with the sapwood in a more or less defined central space but you can find it in very interesting patches on a flat-sawn piece of timber. If you can find sides with some sapwood too it adds nicely to the effect.