canvas: assign white to paint color for texture node
canvas: assign white to paint color for texture node

To get correct premultiplied opacity on a canvas content, white needs
to be assigned to the color that is passed to the texture node. The
content will be very dark for lower opacity values otherwise.

https://bugzilla.gnome.org/show_bug.cgi?id=733385

djdeath/clutter,djdeath/clutter,GNOME/clutter,jigpu/clutter,jigpu/clutter,ebassi/clutter,Distrotech/clutter,GNOME/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter,djdeath/clutter,ebassi/clutter,jigpu/clutter,Distrotech/clutter,Distrotech/clutter,jigpu/clutter,ebassi/clutter,djdeath/clutter,Distrotech/clutter,GNOME/clutter,GNOME/clutter,jigpu/clutter,ebassi/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,ebassi/clutter