I noticed as an Infiltrator I had a light blue shield and as a Vanguard I have a purple shield.
What are the shield colors for each class and what do they "mean"? I assume it's something to do with the balance of combat/tech/biotic each class affords?
Blue are "shields" and purple represents "biotic barrier." Each of your squadmates only has one type, although Shepard's is dependent on his class. For all intents and purposes, the two types are the same when it comes to your defenses.
The specific differences are discussed in an answer to this question:
