Weapon Differences

Here is a quick question: What is the difference in the writing of weapons? I mean, why is somw yellow/gold(rare apparently), some purple, some blue, WHAT IS THE DIFFERENCE!
Also, which is better of the three, and what are each called (aka unique, rare...etc.)

Blue is just unidentified. Use and Identification kit on it to unlock some information about it. Purple is rare.

White is standard, nothing fancy. Blue is the next most common, minor upgrades (precious, salvagable, 10% boosts) very rarely the come with some upgrade component. Purple items are more rare than blue and they have theoretically better stats and upgrades. The yellow/gold items are the most rare and have the best stats/upgrades, again theoretically. Sometimes you'll find yellow or purple items that don't really seem to warrent their color designation. I found a purple item that did nothing but loose the word 'unidentified' when I IDed it. Hope that helps.