Script covers?

Can anyone, with any substantial backing, tell me why I see scripts with the black cover and gold lettering and scripts with a tan cover with black lettering? Is one a first draft the other a second?

I own the tan covered script, but I have seen the Black cover on yourprops.com, and I am wondering why there is a difference? I have seen "Filed" stamps on the black covered ones that might indicate it was filed with Universal officially, but I have also seen the lower right corner numbering for on set use in the tan ones....

Can anyone help me wrap my mind around the two "Official" versions floating around?

I dont know really. Studio copies am sure may have the better covers, but none of them are worth over $50 tops.

I've seen at least three sell for over $300, so that's a matter of what the market can bare I guess.