Why are my audio files white in the timeline?

Hello,

I am new to Premiere so I hope this question isn't stupid.

I recently started using Premiere for video stuff at work.

Normally when I place an audio file into my timeline it appears in a green box but now every audio file I import appears white in the timeline.

Here is a screen shot.

https://www.dropbox.com/s/qcau5z8yw42vwni/screen.jpg

any help would be great.

thanks,

A Premiere Noob