Okay... so I bought a set of 100 RGB LEDs from a guy on eBay (sureelectronics1 - in Shenzhen China I think) and they came with resistors for both 12v and 5v - pretty good deal ($23 including shipping). They arrived in the timeframe expected and they look okay... BUT (and you knew there was going to be one, right?? ) they seem to be working backwards from the way I thought LEDs worked.
I have attached the schematic that was provided on the listing.
When I connect the ground from the power supply to the common cathode (longest lead and if you look inside the LED it's the biggest post) and then connect the positive lead to each of the other leads in turn (through current limiting resisitors) none of the LEDs light. If I reverse the power supply leads so that the postive goes to what should be the common cathode and then I connect the negative to each of the other leads (through the same current limiting resistors) all the LEDs light...
I thought current flowed from the anode to the cathode in an LED... Am I remembering it wrong???
One other thing that's odd is that the long lead is not the second from the right if you have the flat of the LED on the right had side - it's the second from the left.
Edit>> Oops... never mind... I'm an idiot... turns out I ordered the common anode LEDs instead of the common cathode... so now it makes sense! Sorry for the bother...