
Here are two of the most basic methods of choosing colors in FLTK,
and a little bit on applying colors.

The grid displays the 256 indexed colors that FLTK uses.
The tooltip of each square shows the color's index.

In order to provide an accurate visual representation of the color
chosen with fl_color_chooser, color 15 is being set to the rgb
values you pick. The button changes to the new color, as does any
other widget using color 15. The number 15 is an arbitrary one
chosen simply because that color is not being used in the demo.

fl_color_cube is used to find the closest match in the 0-255
range to the RGB color picked with fl_color_chooser. It has a
somewhat complex formula, and I'd probably never use it in a
real-world situation. In fact I probably wouldn't even use RGB
colors as part of a FLTK interface, simply because the indexed
colors are plenty. RGB/hex is of course useful in finding colors
that will be used for other purposes, such as examining full-color
images or passing color values to other programs.
