Solid black would be opaque. Transparent is clear, crystal clear, regardless of whether it's coloured or not. Translucent, as already pointed out, allows light though, but isn't clear, milky plexiglass is an example. I'm not sure what a translucent finish on a guitar would be in the strictest terms. Opaque is solid colour, with no light transmission. In the case of a high gloss black, you (or the CS) could either use a high gloss black medium, like polyurethane, or use a black paint first, followed by a high gloss clear coat, which would be transparent, as you want the black paint to clearly show through.
Now I say I'm not sure what a translucent finish is because of it's very nature. For example, I touched up the Streamer with 2 very light coats of navy blue acrylic paint (I may attempt to recontour it with Bondo yet). While the rest of the finish is coloured oil (transparent) the acrylic paint is opaque. But if you were to paint 2 thin coats on glass and hold it up to thelight you would have a stained glass effect (translucent).