This 1st sun conure in the picture below is being sold as a 'red factor sun conure' and I talked to the lady about it and she said that it will 'color up' with more orange sooner than her other ones, but as an adult they usually look about the same. Hmm, and its being sold for more money. 
Some people/breeders claim 'red factor' if they come across a pair of suns or a chick that has a little more red/orange on them, or get their adult colors sooner than other normal chicks. For the most part these are normal chicks with a little more orange color than other normal chicks. I'm not saying they are trying to deceive customers by selling normal chicks off as red factor, but there is a significant difference in chicks and adults who are 'single factor, red factor'.
Sunkiss below
and Pyro below
Even as chicks, it is very clear to see the difference. If you want a very red sun, I recommend not waiting for a normal chick to 'color up' but buying a chick who has the color you want already. Single factor conures carry that special gene that can be duplicated. In breeding you know what your chances and outcomes are, and you can tell right away when they start feathering if they are single factor.
I suppose the only challenge right now is finding one available... I will post when I come across some available or if mine ever produce. lol
