want to start breeding corns, i am going to get a female at the weekend but dont know what i want to get, was thinking of getting a lavender as love the look of the opal corn
Amel or Ultramel will get you rather different results if you want to produce Opals. You need to know for sure what your current male is, so I suggest going back to his seller and getting a firm identification. Amel would be best for producing Opals with a Lavender.
Amel x Lavender will give you all Normals, het for Amel and Lavender. You then need to keep a male and a female, grow them to maturity and breed them. Normal het Amel & Lavender x Normal het Amel & Lavender will give you a 1/16 chance of producing an Opal. The rest will (statistically) be mostly Normals with some Lavenders and Amels, each with a range of hets.
Ultramel x Lavender will give you all Normals, all het for Lavender, with half of those het for Amel and half for Ultra. If you keep a male and a female, the outcome will be unknown as you won't know whether the ones you kept are het Amel, het Ultra or one of each. If they're both het Ultra or one is het Ultra and the other is het Amel, you won't have any chance of producing Opals.
If your current Amel/Ultramel is a hatchling and you buy a Lavender hatchling, it'll be three years before you can breed them and a further three years before you can breed their offspring. You're looking at a six year breeding project which - if you're lucky - will give you a one in sixteen chance of producing an Opal.
All of those are just the mathematical statistics. It's possible that in a clutch of 20 eggs in 6 years' time, you might get no Opals at all.
This is a really good site to play around with in order to predict morph outcomes of pairings:
http://www.corncalc.com/
i have seen that the opals and other white corns dont sell as much as others with patterns n more colour
Whether Opals sell well, depends on where you live, what's being bred already near you and what sells well near you. There are no real generalisations that you can make. You just need to do the research for your circumstances.
If you already know that they don't sell well then it might not be a good idea to produce them. However things may change significantly in the six years it will take you to get to that point.