Should be in Betta Chat since this sub is more about how to breed but I suppose this is still part of genetics of course
You can ask RussellTheShihTzu to move it if you like!
But Marbling is a big subject, I talk about it a lot on our AquaBid Thread over in Betta Photos. Basically, read through this first: http://www.ibcbettas.org/2012/wp-con...cles/CS-15.pdf
Butterflies are part of the Marble gene so yes, most of them do change, specifically the ones with the white or cellophane band. Ones that have black or blue bands usually are stable in their coloration. Any fish can marble if it has the genes and sometimes you'll never know if it has the genes because it could be a solid blue fish that suddenly turns into a red fish over night practically! It's all a gamble in the long run!
Some Marble types tend to be a little more stable such as a Yellow Koi. With the way the color layers work, this fish tends to be more stable and keep it's colors longer. Again, this is general, you could get a fish that completely goes black or white. On the flip side, a Red Koi is bound to change and the red will take over the black but keep white dragon scales if it has them. Blue is most dominant and will just take over the fish, steer clear from Blue Butterflies if you don't want an all blue fish lol.
Colors are layered as follows from top to bottom:
Here's a really great thread post about the Genetics of color if you're interested: https://www.bettafish.com/showthread.php?t=97189
As for a Betta with a spot of color, it depends on what that spot is. If that spot is blue, chances are that the blue will spread. If it's yellow, it may stay or may get taken over by the other colors on the fish. If it's Red, it will likely take over, may possibly be stable as in the Red Dalmatian coloration. It really depends. If you were to show me pictures, I could give you a good guestimate on how the fish would change or not.
Wilds: Wajok, Rutilans, Siamentorialis, Hendra
Leopards: Luna, Astrael, Dorian, Cullen, Gallifrey
African Fat Tails: Nox and Lux
Bearded Dragon: Stormfly