The most typical color of firebending is orange/yellow flames. However, former Crown Princess Azula's flames were a shade of blue. Blue fire is much hotter and more dangerous than orange fire, just like Azula. She is a very powerful firebender, and that is one of many reasons why she had blue flames.
Ran and Shaw, the last dragons in Avatar: The Last Airbender, could create multiple colors of fire, including pink, green, and purple, along with the normal colors.