I don't know about the legality of them, but I don't think they can be very dark or the police would pull you over right away. Your plate has to be visable or else you might get a fine or something.
I think its the same as windows, they can be tinted to a point but not too dark. I have heard in some states they are illegal so I would double check state laws before buying one (if you are thinking about it).
I am pretty sure they are illegal in my state. I know that you have to be able to read the numbers because you can be given a ticket even if it is just too dirty to read or is covered with snow.
I'm always surprised when I see license plate covers in a pastel color. I would have thought that there would be a law against it but apparently it's legal, as long as the plate is still completely visible underneath.
I did a little looking and it seems that they are illegal in most states, but some allow them as long as the plate is still visible. Definitely check your state law before purchasing one.
I'm glad to hear they are illegal most places. I don't understand how any state could allow them, when it makes it so difficult to see the plate. Even if it is clear, it gets dirty, or has reflections.
While I agree that they should be clear, I don't agree that they shouldn't be allowed. Many of us with personalized license plates use them to protect our plates from damage.