What's the polarity of this capacitor?
On those little plastic rectangle surface mount packages, which are most common for Tantalum capacitors from what I've seen, the grey/white stripe on the end of the package indicates the POSITIVE terminal of the capacitor. 

In the metal "can" style capacitors, and the usual plastic/polymer round cylinder style packages the marking is usually for the NEGATIVE terminal. The tall round cylinder packages often have a grey-ish stripe, with obvious black minus signs going down it. On the metal can packages, the negative terminal is usually indicated by a solid black semi-circle/area of the circle closest to the pin, on the top of the case.

This is from experience, using products with more useful datasheets that specifically mention the polarity markings - and then it's just an industry standard that you'll see throughout your time designing stuff.