When constructing a GdkColor directly, you will need to use the system's color names, hex RGB triples or XcmsRGB values. Attempting to use other formats here will not result in an error message, because the structure itself recognises them, but equally they will not display, because the function doesn't recognise them at all.

The options when directly constructing colors in PHP-GTK are:

<?php
/* XcmsRGB values, expressed as three integers */
$cyan = &new GdkColor(0, 65535, 65535);

/* hex triples expressed as a single string */
$cyan = &new GdkColor('#00FFFF');

/* a color name expressed as a single string */
$cyan = &new GdkColor('cyan');
?>

See also: GtkStyle.