Hey Kenten,
Spearos usually use black masks, cause this is probably the most neutral color matching their wetsuits... And I don't meen it in a fashion way, of course.
When you have a black suit it's good for the mask to be black too cause that way the fish will take your whole body as one thing. And when the color of the wetsuit mathes the surrounding environment, it's difficult for the fish to separate your body from the rocks around which is the perfect camouflage. Recently the top manufacturers started producing masks with reflective lenses so the fish can't even notice the movement of the spearo's eyes.
Now I personally don't think that a dark green mask is worse than the black one if you use a green wetsuit... But the producers usually offer what sells best.
I'd strongly recommend you to give up the idea of bying a transparent skirt mask. The reason is the light that get's through the skirt and into your eyes. You can see it for yourself if you put your hands ina ma mask-like shape over your eyes. You know we see the object because the eye accepts the light reflected from it. So the less sources of direct light into the eye, the better it can focus on the one reflected by the objects. I don't know much about human anatomy, but I think that's the reason. And that's why people wear baseball caps.
