Cloer changes

A friend of mine recently told me she had a blue topaz (or possibly
zircon) ring. She wore it while in a tanning booth. She stated that
it changed into a muddy brown color, but then a few days later
changed back to its original blue color. Has anyone heard of or
witnessed the same? I was under the impression that once changed,
the color was permanent, but had never heard of a stone changing
color in a tanning booth. - Wendy