A dermatologist stated (see link) that "you'll know Tri-luma expired when it changes the color". New Triluma is light yellow. To WHAT does the color change TO when the product expires? For example, my Tri-luma is 4 years past expiry date and the color is still as if bought yesterday (light yellow). Given, I've stored it in the fridge or away from heat at all times. Link: https://www.realself.com/question/houston-tx-long-tube-triluma-fridge