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.