If you are a red head, ie have red hair or orange hair and somehow get an evil twin, they will have blue hair.
However, yellow hair does not automatically result in green hair, it means purple hair.
Determining their eye colour is a lot harder and a totally different, more complex branch of antipodean clone malevolence.
Like blue balls, but it's about your hair
Blue Hair is caused by taking a shower but not washing your hair
...something just doesn't feel complete about it
A girl in an anime where she has a crush on the Main Character. The girl will usually have blue hair of any shade and do anything for the MC. Her feelings will be told yelling at the MC usually around an episode in the teens.
Stacy- "Did you hear what happened to Blue Hair in our studies today?"
Ellie- "No, what happened?"
Stacy- "Oh yea, you have Dojoism studies next period! I forgot lol."