Back to the original question, for most plants, when the pod begins to turn brown (or the fruit begins to color) the seeds are ripe. Color of the seed itself may or may not be an indicator of ripeness, as some seeds do not always change color until dried or exposed to air. Let's see about columbines....
Here are three pods from the same branch on a columbine: #1 is green -- #2 is showing signs of turning brown -- #3 is dehisced (split open).
I snipped the ends of each off. In doing so, also cut into some seeds.
#1
#2
#3
And the seeds removed from the pods -- #1, #2 and #3.
I have to say, the results even surprised me! In this case at least, a completely green pod can have mature seed.
So my advice is snip a bit of the ends of the pod off, and see for yourself what is happening inside.
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RickCorey, I believe that your thin tan seeds were never fertile (or viable) to begin with. I had a difficult time finding a pod with tan seed, and the only viable seeds were either green or black.
The thin, unfilled (non-viable) green seeds (shown by arrows) will turn tan. Unfortunately, when I rolled the pod with tan seed between my fingers to remove the seeds as I did the others, I think the tan seeds broke up significantly. They certainly looked bigger in the pod than when I remove them. In fact nothing came out with this method. I had to slit the compartments longitudinally to extract them.
#2 
#3 
