Cold frame question

Generally the answer would be no to the smoked polycarb. But until you see it, it's hard to say.

the purpose of the coldframe is to acclimatize plants to graduating full light and toughen them up a bit with the cooler temps of an unheated coldrame. The former would be hard to do if the polycarb is a bit too dark. If fairly light, you could get away with it as the plants are in there only for a short time (usually).