Dry-PAC desiccant

How can you tell if the Dry-PAC desiccant is still good? Is there a life expectancy for it? I am kinda new to this game and don’t want to ruin my pcp rifle, I haven’t used the pump much, maybe 15 or so times. Do the little white balls change color when they lose their ability to remove moisture? Just looking for things to look for so as not to ruin my airgun, any feed back from you guys and gals would be much appreciated, thanks in advance!
 
i use desicant in my dryer when i fill my bottles i take and put the dessicantt on a paper plate put in the micowave for about 4 minutes it turns deep blue i let it cool and then put it back in the holder and let my compressor roll i am well over a dozen times as long as it turns blue i am gonna keep using it it turns a little pinkish collar which means its moist.