I don't think the paint would have changed. It's under a layer of clear coat that definitely its still there. You You would be talking about some kind of chemical/molecular change to the paint under the clear coat, which seems unlikely.
Have you given it a good wash recently? I would bet a layer of dirt/grime, even though it's not easily visible, could impact the color shift from the refrecting light. Our old car was a Kia Sportage with "cherry bomb" black because if had red metallic flecks in the paint. When it was dirty is just looked straight black even in the sun. But after a wash the metallic flecks shined again.
I have a Galaxy Grey also, so I'm going to keep a watch on how the paint looks as it accumulates a film of dust and road grime to see if it loses it's purple shift and then wash it to see how if changes.
For any car owner, I would suggest investing in a decent home car wash kit: a decent cheap pressure washer like the $100 one from Home Depot, microfiber towels and wash mats, and good wash soap (no Dawn dish soap) And if you're feeling like it, a good foam canon for the pressure washer. Foam spray the car first to pull off as much dirt as possible before touching the car. Rinse off. Spray a little more foam on. Hand-wash with good wash mats in soapy water. Spray rinse, coat with a spray wax or ceramic coating and Dry with large microfiber towels. You paint will look much better much longer than drive-thru car washes that beat the heck out of paint, and it will be cheaper in the long run.
