What are some cool things I can do to my hair on the weekends that won't get me fired Monday?

I have long light brown hair. I work in a business casual environment. Lately I've been playing with the idea of dying my hair a pastel or blue but my manager quickly shot down that idea. I'm looking for temporary things I can do to have fun with my look on the weekends that will have no trace Monday morning. Last weekend I used a temporary blue dye by Garnier that was supposed to wash out after two washes but took more like 10. It was also super messy and made my hair feel crunchy and dried out. I've thought about bleaching my hair and using a colored toner/conditioner on the weekends but I don't know much about it. Any suggestions?