I think one of the original picture is missing showing the polarity but it is still in the PDF. Anyway, most if not all untrim LED has the longer lead positive/anode. Since the LED is trimmed, you can tell from the body. The lead that has smaller metal surface is the positive/anode. The other side which extends to the middle and houses the LED die is the negative.
Some LED has it reversed, such as the Red LED from me. It's no big deal if you got it wrong, nothing will happen to the LED or the IC driver on the Onion ring.
The next project I am working on is not quite the same so I try not to discuss it here, I will start a new thread when I am happy with the software.