This doesn't answer your question directly, but as Scott Seidman mentioned in his comment, the best way to test any LED is to light it up. You'll want to light them up not only to discover their color, but also to check their brightness and true voltage drop under a given current.
For that purpose, I found this LED tester to be simplest and most useful tool. It's essentially a constant current power supply designed around the LM317L adjustable voltage regulator.
It may features are:
- It lets you set defined current to test LEDs using a trimpot;
- It has a convenient set of test points designed to let you measure voltage and current with a multimeter;
- It also has convenient connectors for you to plug the LED under test;
- Or you can use its pads for testing small SMD LEDs as well.
I keep my tester set for 20mA on my bench and run every new LED quickly through it right after a new batch arrives.