Can JSL use custom Heat Colors?

[#1]

Here's a snippet from a future project.  None of the default color themes do what I want (making numbers at each end black or gray) so I passed a theme definition to heat color for the 2nd argument (instead of the name of a default theme).

colors = Heat Color(
	// the first argument is a JSL matrix for efficiency:
	(0 :: 800) / 800, // 800 pixels wide, smoothly interpolated by heatcolor
	// the second argument is a list that specifies the color theme
	{"", // no name or flags needed, just the name placeholder
		{ // this theme uses 12 colors
			RGB Color( 0, 0, 0 ), // black
			HLS Color( 4.0 / 10.0, .3, 1 ), // darken beginning
			HLS Color( 5.0 / 10.0, .5, 1 ), //
			HLS Color( 6.0 / 10.0, .5, 1 ), //
			HLS Color( 7.0 / 10.0, .5, 1 ), //
			HLS Color( 8.0 / 10.0, .5, .7 ), // desaturate magenta
			HLS Color( 9.0 / 10.0, .5, 1 ), //
			HLS Color( 0.0 / 10.0, .5, 1 ), //
			HLS Color( 1.0 / 10.0, .5, 1 ), //
			HLS Color( 2.0 / 10.0, .5, 1 ), //
			HLS Color( 3.0 / 10.0, .3, 1 ), // darken ending
			RGB Color( .5, .5, .5 ) // gray
		}, 
		// this theme positions the 12 colors between 0 and 1, inset from the ends
		As List( (1 :: 12) / 13 )[1] // positions 1/13 ... 12/13
	} 
);

For( i = 1, i <= 8, i++, // double the height several times
	colors = colors |/ colors
);

pic = New Image( colors ); // matrix to image

New Window( "Demo Heat Color", pic ); // display

Showing the wash of color from Left to Right matching the color theme specification

Here's another approach.