I turned our toilet seat blue!

Casey • 24 year old Marketing professional. Married to a police officer & military officer. Expecting our first, Addison Grace.
Tonight my husband pointed out that our toilet seat is looking blue. After closer inspection I noticed that it has taken the shape of my bottom. I had no clue what this could be. I am wearing the same pair of yoga pants I have had for 3 years. I googled it and it turns out that I'm not the only one this has happened to? Although I can't find an actual answer to why this happens. Anyone else in the same boat?
My husband thinks it's hilarious by the way.