Purple isn't a layer, rather a combination of iridiphores over the red layer, so it is blue and this crossed to a green betta not knowing the background you will likely get a bunch of bicolor bettas.
Between red a blue..I can't stress it enough if people want to breed they should set goals..and try to achieve a good fish, this means form, color and body shape, pet fish are fine but a bunch of them are very hard to get rid of so at least try to breed something that will be easier to sell, just pretty isn't a good thing if you spawn a veil to a HM you will end up with all veils in the F1 a sibling spawn will show you perhaps 25% super delta and that's only if you know what the parents are holding genetically.
If you breed fish, try to stay within the guidelines that breeders follow HM X HM..Ct X CT...Plakat X Plakat..the exception is if you want to strengthen rays in a HM then a cross to Plakat is a good thing IF you know what you are doing.
Most of the fish I have seen on here should not be bred at all, fine if they are pets but the truth of the matter is the pet stores are full of fish that should never be bred..I hav seen some really bad ones on here that people want to try their hand at, while everyon else is on the so cute bandwagon the reality factor is a little harsher.
I'm guessing you are either talking about red with irid or lavender.
The former will give you more red-irid combinations, while the later will give you more variety of color combos - multi irid, darker lavender, lavender, cambodian like patterns, plus a few more. This is just probability - what you actually get depends on genetic background.
If you want to cross multi rays (HM) to double rays (VT), try using a HM female. You will not produce HMs in F1, but you should have some deltas or at least VT with wider spread. Then you work yourself towards HM. It will take you at least 3 generations.
HM x HM DOES NOT = 100% HM. If you have a pair from a good line, you might produce 60% (or more) HM. But breeding poor HM genetics will only give you a few true HM. Most will likely be Super Delta.