I suggest latex. You will need to clear coat it to make it fuel proof. Here is a basic "How To" for latex (RC Universe is STILL giving me fits about uploading files).

Painting with Latex


First, if you have not done so, I strongly recommend you read the article
by Roy Vallencourt on using latex paint.
http://www.modelairplanenews.com/how_to/latex1.asp

I do disagree with Mr. Vallencourt in a couple of areas. These areas
of disagreement are based on my personal experience using latex.

1. I add 1 1/2 caps of FloTrol per quart of latex paint PRIOR to any
diluting. The Flotrol retards the drying slightly and allows the paint
to level itself.

2. Use ONLY water for thinning the paint. My experience has shown
that using windshield washer fluid gives a slight tint to light colors.

3. My best results with latex have been between 25 psi and 30 psi.
Under 25 psi I don't get the coverage I would like and over 30 psi the
paint starts to have a "dimpled" appearance.

4. I have not had good luck using a heat gun to promote quicker drying.
I know of several people who have had good luck using this technique
though. You can try it and see if it works for you or not.

5. I strongly suggest and highly recommend the blue 3M brand of masking
tape. What you want is the "60 Day Safe Release". This can be
identified by a paper appearance to the tape and on the side of the
wrapping is an adhesive index. You want a 2 dot adhesive rating. The
2 dot adheres reasonably well, yet will not pull up even fresh underlying
paint.

6. Flat latex will take an average of 7 - 10 days to "cure". Semi gloss
and gloss latex take 14 - 21 days to cure. To see if the paint is cured,
press your finger firmly on a hard area of the plane (I use the cowl
area). If a fingerprint remains, the paint is not cured. The
fingerprint will disappear in a day or two.

7. Gasoline powered planes will be fine with the paint as is. Glow
engine powered planes need to be clear coated. I suggest waiting until
the latex is cured before clear coating.

For clear coating I suggest one or 2 sprayed coats of a water base
polyurethane. My personal experience has shown that it is fuel RESISTANT
to 10% nitro and various reports indicate no problems with 15% nitro.
By fuel resistant, I mean if you let the clear coat dry for a minimum
of a week before exposing it to fuel AND you clean your planes at the end
of the day,you should have no problems. If you let the residue sit
overnight on the plane, it will become sticky. If you want fuel proof,
use Ultracote or Lusterkote clear. Oil Base polyurethane is also fuel
proof, but it will start yellowing in about 6 - 8 months. The yellowing
is not that noticable on dark colors, but very noticeable on light colors.