I agree about the chlorphyll. When the seedling is large enough to start feeding the nitrogen should green it up. If not, something else is wrong like shorerider stated.
It honestly depends on the source. Ive had some Brains that werent all that hot and Ive had some brutal Brainstrains. Its all about the source. Another example is the Trinidad Butch T Scorpion. Id never had a really hot one until I ate one that was sent from Butch Taylor.