Tiffen screw-in filter are made of green glass (the glass looks green when viewe d from the edge). Their large professional-grade filters use clear glass (also k nown as water glass). Does anyone know if clear glass is really better than gree n glass? Is there a reason to spend twice as much for clear glass? I know Heliop an and B+W use clear glass, but they do not make all the colors that I want (58, 47, 47b).