## 1.52.17 colormap

    set colormap <color expression> [ mask <expr> ]

The setting `colormap` is used to specify the mapping between ordinate values and colors used by the `colormap` plot style. Within the color expression, the variables `c1`, `c2`, `c3` and `c4` refer quantities calculated from the third through sixth columns of data supplied to the `colormap` plot style in a way determined by the `c<n>range` setting. Thus, the following color mapping, which is the default, produces a greyscale color mapping of the third column of data supplied to the `colormap` plot style; further columns of data, if supplied, are not used:

    set c1range [*:*] renormalise
    set colormap rgb(c1,c1,c1)

If a mask expression is supplied, then any areas in a color map where this expression evaluates to false (or zero) are made transparent.