COLOUR INHERITANCE IN BETTAS 
There are four layers of color--the yellow is the bottom most, then black, red, and the iridescent layer is upper most. 
Colour Genotypes, notation: 
[+ denotes wild or "normal" form; upper case denotes dominance over +; lower case denotes a recessive or semi-dominant trait.  Thus, ++ or +w or w+ give normal coloured eyes and ww gives white eye.) 
  
w  white eye  recessive white outer ring to the eyes. 
c  Cambodian  recessive limits black 
b  black or m melano recessive black males; deadly in females. 
Si  spread Iridocytes dominant causes spread of iridescence over body and fins 
Op  opaque  dominant produces an opaque, white coating on the body and fins; present in all pastel colours. 
bl  incomplete dominance metallic blue-green iridescence* 
Bl incomplete dominance green iridescence* 
nr  non-Red recessive removes red; present in yellow, white and some Cambodians 
b  blond  recessive dilutes colours by reducing melanin;  
L  red-Loss dominant all red colour fades as the fish matures, revealing the other colours if present. 
mb  marbled pattern  recessive colour blotches 
Vf variegated fins dominant streaked fins and butterfly trait  
ER (or R ) extended red  dominant all red, colour varies from cherry red to vermillion, depending on other factors present. 
*N.B. the Bl & bl alleles determines steel blue, blue-green, turquoise, corn-flower and royal blue colours.  Blbl or blBl gives royal blue, BlBl gives green and blbl gives steel-blue.