The pods need to be brown and the seeds will be black when they are ripe. The pod will pop open at the top when the seeds are ready to fall, but you can collect the unopened pod if it has turned completely brown - the pods on mine are so dark they are almost black.

Becky

I've also found that on some of the early pods, there are no good seeds inside. This often happens with a plants first blooms. So that could be what has happened to you. The ones developing now are probably filled with good seed and you will find them in the soon to be ripe pods.
Remy

The seeds I have look like fuzzy B Bs and about the same size. I collected them from plants at our local town hall. The seeds are deep inside the pods.