Supply and demand. Nice female pastels are always in demand, but due to the quantity of them being produced, can only fetch a price of $200 or so for even very exceptional examples. On the other end of the spectrum, male bananas were going for as much as $50-60,000 earlier this year because there were only a handful of them known to be around.
The odds of hitting certain morphs affect the price as well. If you're selling a double recessive animal, that was likely a project that took years to complete, and therefore can command higher prices.