In the following example, the surface and the color function are specified by procedures.
>

$f\u2254\left(x\,y\right)\mapsto 7\cdot \mathrm{sin}\left(\frac{x}{2}\right)+4\cdot \mathrm{sin}\left(\frac{y}{4}\right)$

${f}{\u2254}\left({x}{\,}{y}\right){\mapsto}{7}{\cdot}{\mathrm{sin}}{}\left(\frac{{x}}{{2}}\right){+}{4}{\cdot}{\mathrm{sin}}{}\left(\frac{{y}}{{4}}\right)$
 (1) 
>

plot3d(f, 0..20, 0..70, color=proc(x,y) x*y end proc);

In this example, the the surface and the color function are specified by expressions.
>

$\mathrm{plot3d}\left(\mathrm{sin}\left(x\right)\,x=0..8\,y=0..8\,\mathrm{style}=\mathrm{surface}\,\mathrm{scaling}=\mathrm{constrained}\,\mathrm{color}=\left[\mathrm{sin}\left(xy\right)\,\mathrm{cos}\left(xy\right)\,0.8\,\mathrm{colortype}=\mathrm{HSV}\right]\right)$

>

$\mathrm{plot3d}\left(\mathrm{sin}\left(x\right)\,x=0..8\,y=0..8\,\mathrm{style}=\mathrm{surface}\,\mathrm{scaling}=\mathrm{constrained}\,\mathrm{color}=\left[\frac{x}{16}\,\mathrm{sin}\left(xy\right)\,\mathrm{cos}\left(xy\right)\right]\right)$
