So I kinda wanna dye my hair blue over winter break and have it last for the duration of winter break: Dec 15th - Jan 15th. I don't really wanna have it died while I'm in school because it's business school, my senior year and I don't think blue hair would fly well with many teachers.
This is pretty much my normal hair color:

This is my hair in the sun:

This was my hair 4 years ago with a very subtle red dye:

Any good ~4 week dye suggestions?