The only "purple lines" I remember are either the "scope indicator" (don't know the official name), which shows the scope of the block the cursor currently is in, and the Quick Diff inidicator, which indicates lines that have changed against the file on disk/in the repository (based on your quick diff settings).
Does Eclipse show some additional information when you hover the mouse over it?
Can show us a screen shot?
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus
author & internet detective