"Space used" line is red for my dvd drives(???)

[snorkyller]

I have Windows 7
In the "Computer" window, each unit has there's a line representing the space used, and for my DVD drive, this line is red when one particular dvd is into it. What does it means?

 

[Laquer Head]

most likely indicating the disc in question is full or darn close and cant hold any more data!