Is there any reason a one pence coin should look lighter? I saw one today that had been dropped. I pocketed it. Looking at it now it immediately seemed lighter in shade than I would have expected. Compared to another it looks lighter and it sounds a little different when dropped onto my desk. Any reason why this would be the case?

Sometimes coins are made of the wrong alloy in the mints, I've often seen on eBay nickel "coppers".
What is the year of it?

Both pictured are 2007

EDIT: Just a theory, could this perhaps be some kind of error during the copper plating of the steel? Perhaps resulting in a lack of copper in the coin?

Could well be!

This guy should be of more assistance, email address at bottom of page.

A nice, friendly guy who's very knowledgeable in his field of errors.

http://www.worlderrors.com/

Clive.

I actually think I have a few of these now. Mabey they are planning a slightly different alloy allong the new coins?