GtkTooltips::set_colors

void set_colors( GdkColor background , GdkColor foreground );

This method is deprecated. Colors can be set via styles.

This method sets the foreground and background colors for the tooltips.

On linux this method doesn't work. Use the styles instead.

Ejemplo 48. How to set the color of tooltips

$style = 'style "tooltips" { bg[NORMAL] = "#ff6060" } widget "gtk-tooltips" style "tooltips"';
gtk::rc_parse_string( $style);