You can add a mildew/fungicide to ANY paint,I beleive flat paint is much(alot) better at reflecting light than gloss or semi gloss and there is a paint that is supposed to be more reflective than others but i cant recall the brand(paint store like dunn edwards or something)but i do remember the color was titanium white.
If you put a gloss on it will be matt quality soon. I have found it you plan on more then 1 or 2 cycles the finish is not all that important. If I was buying paint I like the reflection off a matt finish the best. JK