Crystal malt is still barley and, therefore, not GF. The only GF grains commonly used in beer brewing (off the top of my head) are corn, rice, and oats. And even oats are a stretch as it contains a "type" of gluten that most celiacs don't respond to, but some do. Sorghum seems to be the standard base grain for GF brewing. For color and flavor, I've heard of some GF brewers using specialty rice (wild, etc.), but that would take some experimentation.