(nitro)lacquer is lacquer.....colored or clear it reacts the same way to polishing/finishing. most opaques don't use a clear you just layer up the color and do your sand and polish accordingly. any type if pearl or flake does need a clear for obvious reasons and like mentioned above, solids do look deeper with clear and the flexibility of repairing a clear coat ding is much easier imo. automotive poly paints are another story in that they HAVE to be cleared, they are much more durable, less shrinkage, more colors, ect to choose from but alot of people here wouldn't use this on a musical instrument. The debate on tonal damping effects is prevalent, obviously a large majority of the top manuf. use these type of paints and make good to great sounding guitars. I just aquired an older USA Washburn, and the factory poly finish is impressively thin and this guitar sounds and sustains as good as any high end boutique guitar I've played. I believe thickness to be more important than finish type in how it might affect tone imo.