From BJCP description ( http://www.bjcp.org/2008styles/style19.php#1c ):
Ingredients: Well-modified pale malt should form the backbone of the grist. Some specialty or character malts may be used. Dark malts should be used with great restraint, if at all, as most of the color arises from a lengthy boil. Citrusy American hops are common, although any varieties can be used in quantity. Generally uses an attenuative American yeast.
basically anything other than dark/roasted malts, usually varied crystals, honey, or toasted malts. technically its just not fitting of style, but part of the fun of homebrewing is doing what you want, so you certainly can use it if you want