Different kinds of clips are different colors. (Audio, video, stills, etc.)
They're NOT different clips though. They are the exact same type of clip. Both are MP4 videos from a Sony EX1. There's nothting different about them other than the color on the timeline.
This is a bug that has been around since Media Browser (MB) was introduced in CS4. Sometimes this happens, sometimes it don't.
If you import the file from MB directly to the Project panel it works ok most of the time, sometimes it don't. However, if you double click the file in MB and thus open it in the Source and then drag the media to the Timeline it happens very often, ie that the clips come in with one color for the video and one color for the audio. I have never been able to reproduce it to 100%.
It has nothing to do with different kind of clips since the clips imported are A/V.
I have seen this with captured HDV.