Unnatural hair colors is the new norm. Practically anywhere you go in the city is guaranteed to have at least one person with dyed hair. I personally have changed colors three times in the past year. Having freshly dyed hair is an amazing feeling, but you walk out into the world just to be met with criticism and assumptions. People will assume that it is for attention. While that is a possibility, there are many reasons why people would dye their hair.
1. Their natural hair color does not fit their personality.
Many people use their clothes as a way of expressing themselves. People who dye their hair are trying to do the same thing. Imagine being the type of person who preferred bright happy colors, and only being able to sport dark grays and blacks. You would be frustrated with your appearance. That's how I personally feel when I have my natural brown hair.
2. It is time for a change.
After a major change in your life, it is nice for a bit of the old "out with the old and in with the new". Buy a new wardrobe, maybe go on a vacation. Sometimes seeing a new you in the mirror can be just the same.
3. It looks cool.
Dying your hair doesn't have to have explanation. People can bug you about why you chose the color that you did, or how they think you should have done it. At the end of the day, it is your own choice. You don't owe anyone an explanation for what you chose to do with your own body.