The prominence of Blue color is the extension of the Blue stripe on the saree of Mother Teresa. White is the color of peace and that's what Mother personified. 

The artist has maintained the simplicity and aura of the noble Lady who dedicated her whole life to humanity. 

The two shades (white and blue) sums up her life and work. 

Mother Teresa won The Noble Prize for peace and her service to mankind. After her death she was also cannonized (given the title of a saint by Pope).