Sounds like BS to me. The color has more to do with how much light is in the room and how much air can get to the flame. Methanol will burn a hard to see bluish flame in bright light, but a bit orange in dim light. More air more blue, less more orange. Just like natural gas, a blue flame indicates proper mixture. I think the dye used in the oil would have more to do with this than the flame. Some are known to change color in bright sunlight, making the use think the fuel has gone bad. Most US synthetics are one of the UCON brand oil, a polypropolene gycol based synthetic. Note that it's clean burning, while castor oil only partially burns.

http://www.dow.com/polyglycols/ucon/products/2cycle.htm