Based on information in “Camouflage en Kentekens“ the Hansa-Brandenburg painted according to the standard prescription for the Imperial German Navy in April 1918.
All horizontal surfaces visible from above should be provided with regular hexagons with sides of 15 cm and grey colours blue, brown and grey violet.
The other surfaces should be painted in a gray-blue hue.
Surfaces on the bottom should be provided with a light blue tint or linen coating kept the natural linen colour.
Everything had to be finished with lacquer.

Hansa-Brandenburg W.29 was fitted with wings regular hexagons, the floats and styles were probably covered with black tar varnish. The hull was light blue grey.

"Camouflage en Kentekens..." lists the German colour Light with the "transcription" listed below (see table)
I am not sure whether this is the same as the colour of the then German Navy used for its aircraft.

Scheme Colour name FS-number BS-number Humbrol XtraColor Vallejo Model Color Vallejo Model Air
Standard Fuselage Light blue-grey - - 162 X257 - -
Undersides of wings matt doped linen     74   - -
Uppersides of wings and fuselage German Naval "lozenge": a pattern of hexagonals.         - -

Check www.paint4models.com for an extensive conversion table with lots of colour and paint systems.

Kleurenschema HansaBrandenburg W.29 Marine Luchtvaartdienst
Colour scheme HansaBrandenburg W.29 Royal Netherlands Naval Air Service might have looked like.