Drawing graduated colour fills in Postscript

%
% draw shape
%
1 inch 1 inch moveto
2 inch 1 inch lineto
2.5 inch 1 inch 0.5 inch 180 0 arc
4 inch 1 inch lineto
4 inch 2 inch lineto
3.2 inch 2 inch 3 inch 3 inch 2.5 inch 3 inch curveto
2 inch 3 inch 1.8 inch 2 inch 1 inch 2 inch curveto
closepath
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% fill
%
gsave % save path for re-use
clip % set path as a clipping path for our infill
3.5 inch 0.5 inch translate % origin to bottom right
45 rotate % so fill is diagonal
Step setlinewidth
/s 3 inch def
0.05 1.0 0.8 StartHSB
0.19 1.0 1.0 EndHSB
1 Step s {
StepHSB
newpath
-2 inch exch moveto % position left hand side
4 inch 0 rlineto % draw a line
stroke
} for
grestore % restore path
%
% draw outline of restored path
%
3 setlinewidth
0 0 0 setrgbcolor
stroke

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% functions
%
/inch { 72 mul } def
/dpi { 72 div } def
/Rez 150 dpi def % calc lines per point for fill
/Step 1 Rez div def
/StartHSB { /B1 exch def /S1 exch def /H1 exch def } def
/EndHSB { /B2 exch def /S2 exch def /H2 exch def
/Steps s Step div def
/Hstep H2 H1 sub Steps div def
/Sstep S2 S1 sub Steps div def
/Bstep B2 B1 sub Steps div def
} def
/StepHSB { /H1 H1 Hstep add def
/S1 S1 Sstep add def
/B1 B1 Bstep add def
H1 S1 B1 sethsbcolor
} def