Sorry - bit late but here goes:
No information on Singapore Schemes in Warren P Russell's book
The following information comes from The Golden Age of NZ Flying Boats by Paul Harrison:
Notes plus an ExtraColour Cross Reference Chart
Short Singapore III
"When these flying boats were taken over at Seletar, they were painted in standard RAF Coastal Command scheme of the period: upper wing surfaces, hull and floats Dark Sea Grey and Extra Dark Slate Grey. The undersurfaces were painted Sky Blue.
The roundels were Type B upper mainplane, Type A under the lower wings and Type A1 on the fuselage. RAF standard fin flash were carried on the outer surfaces of the outboard fins (see Robertson 1966).
Standard serial numbers in eight inch black were painted high on the rear fuselage under the tailplane.
The squadron codes ‘OT’ were issued after arrival in Fiji. This and individual letters were painted in Sky Grey.
Individual letters allocated to the aircraft were K6912:A, K6917:B, K6918:C."
ExtraColour Cross-reference Chart for Singapore III
Upper Surfaces: X 25 Dark Slate Grey, X5 Extra Dark Slate Grey
Fuselage: X 25 Dark Slate Grey, X5 Extra Dark Slate Grey
Lower Surfaces: X7 Sky Blue
Roundels / Fin Flash: X11 Identification Yellow, X30 Roundel Blue, White, X31 Post Office Red
Serial: X 12 Black
Codes: Sky Grey
Hope this helps
Tony