variable color

In Metapost (or rather in Metafun) one can define arrays of colors, strings, paths, pens and other variables. An example is the following:

\starttext
\startMPpage
	string MyColors[] ;
	path   MyPaths [] ;
	pen MyPens[] ;
	for j = -1 step 1 until 3 :
		MyPens[j] := pencircle scaled ((2+j)*pt) ;
	endfor
	MyPaths[-1] := (-1.5cm,1.5cm) -- (1.5cm,1.5cm) ; MyColors[-1] := "magenta" ; 
	MyPaths[0] := (-2cm,2cm) -- (2*cos(0)*cm,-2cm) ; MyColors[0] := "darkyellow" ;
	MyPaths[1] := fullcircle scaled 3cm ; MyColors[1] := "darkred" ;
	MyPaths[2] := fullsquare scaled 2cm ; MyColors[2] := "darkgreen" ;
	MyPaths[3] := (-2cm,-2cm) -- (2cm,2cm) ; MyColors[3] := "darkblue" ;

	for j = -1 step 1 until 3 :
		draw MyPaths[j] withpen MyPens[j] withcolor MyColors[j] ;
	endfor
\stopMPpage
\stoptext

In the above example, instead of

string MyColors[] ;

one could have said

color MyColors[] ;

and then we should have defined each component of MyColors as colors instead of strings:

\starttext
\startMPpage
	color MyColors[] ;
	path   MyPaths [] ;
	pen MyPens[] ;
	for j = -1 step 1 until 3 :
		MyPens[j] := pencircle scaled ((2+j)*pt) ;
	endfor
	MyPaths[-1] := (-1.5cm,1.5cm) -- (1.5cm,1.5cm) ; MyColors[-1] := magenta ; 
	MyPaths[0] := (-2cm,2cm) -- (2*cos(0)*cm,-2cm) ; MyColors[0] := darkyellow ;
	MyPaths[1] := fullcircle scaled 3cm ; MyColors[1] := darkred ;
	MyPaths[2] := fullsquare scaled 2cm ; MyColors[2] := darkgreen ;
	MyPaths[3] := (-2cm,-2cm) -- (2cm,2cm) ; MyColors[3] := darkblue ;

	for j = -1 step 1 until 3 :
		draw MyPaths[j] withpen MyPens[j] withcolor MyColors[j] ;
	endfor
\stopMPpage
\stoptext

Also note that in order to specify the size of the pen in MyPens[j] we have to say ((2+j)*pt) in order for Metapost to interpret correctly the desired size of the pen. The outer parentheses are to prevent MetaPost from interpreting the definition as

MyPens[j] := (pencircle scaled (2+j)) * pt ;