)).
Alternatively, the using specifier can contain an expression that evaluates
to a 24-bit RGB color as in the example below.
Text colors are similarly set using tc rgbcolor variable.
Example:
# Place colored points in 3D at the x,y,z coordinates corresponding to
# their red, green, and blue components
rgb(r,g,b) = 65536 * int(r) + 256 * int(g) + int(b)
splot "data" using 1:2:3:(rgb($1,$2,$3)) with points lc rgb variable