The answer is yes, if it stabilized. I gave my daughter a turquoise pendant a couple years ago. She is not really a turquoise enthusiast, so she rarely wore it. In fact most of the last two years, the pendant was hung on a jewelry tree on her dresser. The jewelry tree was exposed to direct sunlight through the window in her bedroom. The glass in the window increased the heat the pendant was exposed to. Last week, she texted me a picture of the pendant and asked what happened. She brought the pendant to me and I put it under my loop to try to discover what happened. My observation clearly showed a brownish discoloration that penetrated into the stone. The part of the stone that did not have direct, constant sunlight remained a robin’s egg blue.
Since 90% of all turquoise on the market today is at the least “stabilized”, my recommendation is to not let your turquoise jewelry be exposed to intense sunlight for long periods of time. Place your pieces in a place that will protect it from sunlight and heat.
note: Stabilization is a process where rough turquoise stones are heat treated with resin to enhance the color and hardness for ease in creating polished stones suitable for mounting. This is a standard practice today, and most turquoise jewelry purchased today will be stabilized. This includes most higher end shops.
Stabilized stones will not change color over time if they are properly cared for. Natural, untreated turquoise does turn color over time due to the porosity of the stone. Body oils, hand lotions, soaps, etc. will effect them. My experience is that natural, untreated stones will go from blue to a greenish blue.