one of the documented procedures in this installation of the ACS
css_html_color_name_p   font_name
What it does:
returns 1 if font_name is one of the html defined font names and returns 0 otherwise
Defined in: /web/philip/tcl/display-defs.tcl

Source code:

    if { [lsearch -exact { white silver gray maroon green navy purple olive teal black red lime blue magenta yellow cyan} $font_name] != -1 } {
	return 1
    } else {
	return 0