The abstract data type Colour, implemented in the module
Geometry.htmlGeometry, represents colours in
HTk. Just like distances, the type itself is abstract, but unlike
distances, there is a class ColourDesignator allowing
colours to be specified in a flexible manner by overloading. Functions
expecting a colour as an argument take any instance of
ColourDesignator as argument, such as
which set the background or foreground of any interface element which
has a colour (nearly all). Its main instances are:
The strings are named colours (red, white,
black, etc.), the tuples are RGB values. (The functions of
the type classes HasColour and ColourDesignator are
for HTk's internal consumption only, but annoyingly appear all over
the documentation.)