The desiccant powder I use has blue crystals in it. At least, they are blue when the powder in new. As the powder is used the crystals turn a light tan and loose their ability to absorb moisture.
So at the beginning of each season I put my desiccant power in the microwave and zap the crystals back to blue. I dump the powder onto a paper towel and put it in the microwave. 30-seconds – check it. 30 more – check it. After a bit the crystals turn blue again. Be careful the powder and crystals get hot.
You can see both tan and blue crystals in the attached photo. (they were all tan before I zapped them)