ISAF published three complementary documents (and not only one ;)) you can check here:
http://www.sailing.org/2129.php

-first is interpretation, in order to prepare the second one:
-second is amendment
-third is class rules up to date

The second text (amendments2012) is the key one. The main point is paint on hull.
ISAF text is clear and confirmed last world council clarification:

"The following amendments to the Class Rules have been approved to be effective 21th February 2012.
Rule C.7.2
Amendment: Add new rule to read as follows:

C.7.2 MODIFICATIONS, MAINTENANCE AND REPAIR
(a) Holes not bigger than necessary for the installation fittings and passage of
lines may be made in the hull.
(b) Sealing strips of any suitable material for centreboard/daggerboard slots are
permitted.
(b) Routine maintenance such as painting and polishing is permitted without re- measurement and re-certification, providing that the intention and the effect is to polish the hulls only.
(c) Each hull shall have at least one inspection hatch. All other fittings are optional

Rule D.2.3
Amendment: Delete rule and renumber accordingly.
Rule D.3.1
Amendment: Add “polyester gelcoat” after “glass fibres” so the rule now reads
as follows:

D.3.1 MATERIALS
(a) The hull shells shall be built from polyester or vinylester resin, glass
fibres, polyester gelcoat, a core of PVC, balsa or felt, the combination of wood-epoxy, injected plastic, which shall not be altered other than locally for fittings, and passage of equipment and normal reinforcement. Epoxy glue is permitted for joining components. Every material that is not expressly permitted is prohibited.

END"

In a few words: boat maker have to used polyester gel coat, paint can be used for repair only under responsability of sailors (that's why ISAF moved the item in the class rule).
So painting an entire hull, isn't "routine maintenance" and obviously breaking the rules.