Go wikipedia:
http://en.wikipedia.org/wiki/Supermarine_Spitfire_%28late_Merlin_powered_variants%29 Beware though: The picture shows the MK.IX not the MK.V: Look at the exhausts and the wider fin
The MK.IX floatplane did not go into service, there was only one built. It was intended to be used in the Far East T.O.W. and only some 30 kts. slower than the land based counterpart, but plans did not realise.
Paint scheme was standard, but like every prototype and experimental aircraft it had the undersides painted in trainer yellow. Serial was MJ892. I do not know when the alternating "A" and "B" paint schemes were discarded, but if still in use it had to have a "B" paint scheme.
The MK.IX had a wider chord fin and the usual differences between the MK. V and MK.IX, otherwise it looked quite similar concerning the floats and the ventral fin, so no problem to use the parts on a MK.V IMHO.
I like the Spitfire floatplane too. In "Sigh for a Merlin" Alex Henshaw expressed his regrets never to have flown one, since this probably was the Spitfire variant he would have liked most.
I am a bit into "What if" modelling and I wonder what a later day Schneider trophy racer based on the MK.IX floatplane with the Speed Spitfire canopy and a paint scheme similar to the S.6B would have looked like!
Greetings, Martin