Sourceforge: https://sourceforge.net/projects/tcl-yacp/
bll 2020-8-19 : Now available on Sourceforge. RGB, HSL or HSV. 16, 24 and 32-bit colors.
bll 2017-4-23 : I dislike the default color picker that comes with Tk, and the other implementations did not appeal to me. I wrote a simple HSV color picker. It's not difficult to make this work with RGB or HSL (and I believe I have code available if you want it), but I don't think I ever got CIELUV working. 2018-1-2: reordered pre-selectable colors. 2018-4-22: added HSL and RGB.
yacp.tcl accepts the initial color from the command line, and outputs the new color (or initial color if closed) to stdout.
Examples:
tclsh yacp.tcl # defaults to HSV tclsh yacp.tcl -model hsl tclsh yacp.tcl -model rgb # (-mode dynamic) same as Tk's color picker. tclsh yacp.tcl -model rgb -mode static '#80a0a0'