After completely drying filament in a dryer and then vacuum sealing it in a zipper type vacuum bag with 50 grams of color changing desiccant per spool.
In the future, if none of the dessicant has changed color, can I be confident that the filament is still dry and doesn’t need to be put in the dryer again?
I live by the old Ronald Reagan motto “trust but verify”.
So you’ll likely get a lot of great replies here. But don’t take anyone’s word for it. Go find out on your own. Here’s one method which you can do with a simple kitchen scale and zip lock bag.
Now if you don’t have a new desiccant bag, you can always take one and dry it in the oven at 40-50C or 100-120F. Give it two hours and they should be “dry enough” to at least measure a moisture difference.
Just remember your high school or college chemistry. 1g=1ml=1cc of water. I love the metric system!!!
Based on that small experiment, you will not only be able to prove that the desiccant you purchased isn’t just clay and sawdust but you’ll also know empirically just how much water absorption it’s capable of. You’ll also have the satisfaction of doing it yourself and knowing you got a straight answer and not some marketing hype off a box.
That’s a great suggestion. I could even measure it at different points like when I first notice a few change color until it all changes color.
Exactly!!! That’s one of the fun things I feel make this hobby someone unique. You get to be an armchair scientist and test things for yourself but there is no homework to hand in. 
Weigh the filament and dry it until it stops losing weight.
Record the weight of the dry filament before you seal it in the bag.
If it weighs the same when you take it out, it is still dry.
If it has gained weight (moisture), the desiccant presumably has also, so they both get dried again.
That would be a good thing to do as well.
What I would probably want to do is always weigh it at first and if a time comes where it weighs more than it should, then I could see whether or not the dessicant changed color at all. If the filament has moisture but the desiccant hasn’t changed, then that would tell me that it is not a reliable indicator, whereas if it did change, I can save myself the extra step of weighing the filament in the future.
I guess I could do an accelerated test by leaving some filament and desiccant out in the open.
Color changing desicaant typically changes when about 50% of its capacity to hold water has been reached, which means between 0 and 50ish percent will appear visually the same. Using weight is going to be much more accurate as described above if you want to be particular about it.
I do a similar system where every roll, even pla, is individually vacuum sealed with color changing desicaant. Since I don’t tend to have moisture problems after drying and storing in this manner, I have not bothered to track potential hydration over time.
I think you are all taking about indicating silica gel, which is a effective, low-cost and convenient to use desiccant. With that said, there are more effective desiccants. The CaCl2 desiccant that Bambu supplies with the AMS is one example: it will actually suck moisture out of silica gel in a closed container.
In my experience here in Florida - where it’s normally about 50% humidity inside an air conditioned office or home - a perfectly dried filament stored in an airtight container with silica gel will show no more than about 12% humidity no matter how long it’s stored. That’s plenty dry enough for 3D printing.
But if you are OCD and want the humidity figure lower, use CaCl2 or molecular sieve desicciants.