[NTG-context] cmyk in metapost

26 Jun 2011

      I must be doing something wrong. But what?

Relevant part of Metapost code:

numeric Cb, Cr, Y, T, temp, graycolors;
Cb := 0; Cr := 1; Y = 2; T := 3; graycolors := 15;
numeric colors[][];for i = 0 upto graycolors:
	temp := (graycolors - i) / graycolors;
	colors[i][Cb] := temp; colors[i][Cr] := temp; colors[i][Y]  := temp; colors[i][T]  := 0;
endfor
def colorvalue(expr v) =
	cmyk(colors[v][Cb], colors[v][Cr], colors[v][Y], colors[v][T])
enddef;
for i = 0 upto 15:
mycmyk[i] := colorvalue(i);
endfor
Used with drawdot... withcolor mycymk[index];

The error from metapost is in the generation of the cmyk colors:
! terminal: >> (redpart mycmyk0,greenpart mycmyk0,bluepart mycmyk0)
...
...
(1,1,1,0)
! Equation cannot be performed (color=cmykcolor).
<to be read again> 
                   ;
 mycmyk[(EXPR0)]:=colorvalue((EXPR0));
                                               ENDFOR
startsubtitle->...:mycmyk[i]:=colorvalue(i);endfor
Strangely the following does work without problems:
drawdot... withcolor colorvalue(index);

I got the code from the Metafun manual. Beta from ConTeXt  ver: 2011.03.28 01:03 MKIV download.
Something obvious I am overlooking?

Hans van der Meer