Crystal Healing

I got this necklace, as a gift.
When i first got it, it was a Purple type color.
After awhile when wearing it, my mom pointed out that it was a light blue color.
I spent the whole day watching it, and sometimes, depending on the light, it was purple, sometimes it was blue and other times it was both.
The necklace is from Czechoslovakia, and on the back of it,
it says in very small wording " Jay Flex Sterling " .
Does anyone know what this gemstone is?