Cooper,is a unique color ,one of my favorite color in my collections.So,i took an article from to share with u guys the information about this type! so enjoy!

The now so popular copper color and "mask" characteristic are both developments which were created by crossing Betta splendens to Betta mahachai and/or Betta imbellis. The latter two species naturally have a higher degree of iridescence on the scales to compensate for the murkier waters of their native lands [8].
Outcrossing these species to betta splendens and selective breeding resulted in true breeding hybrid plakat bettas which were called 'copper imbellis'. These fish possessed two new features; (1) metallic scaling and (2) masking.

By selective breeding, the Asian breeders succeeded to develop the copper imbellis into a longfinned line and selectively breeding lead to a heavy and thick metallic/copper color and a masking which was more or less covering the head.
The typical metallic/copper sheen is caused by the crystalline layer. Whereas in classic blue-green the iridophores are all the same size and shape, metallic iridophores are characterized by different shapes and sizes. Because of this the crystaline layer influences the refraction of the light spectrum which could be an explaination for the color changes which sometimes can be observed in metallics.

The copper/metellic color and the "mask" characteristic are distinct traits which both are inherited by intermediate (partial) dominance. Crossing copper to a normal blue (non-metallic) will give metallic blues in the first generation (F1) with a chance of getting copper back in the next generation (F2). The same accounts for the mask characteristic. When a full mask fish (homozygous mask) is paired with a non-masked fish this can lead to heterozygous mask offspring (F1). Keep in mind here that the degree of masking will greatly differ in the offspring, some will show some masking while other don't show it. The next generation (F2) will give you fish with more masking signs or maybe even some full masks. I think selection also plays a great role here.
Still a lot of experimenting can be done with these relavitely new traits. These traits can be combined with other colors like blue, melano, opaque, red, yellow, etc. Both traits influence all other colortypes and the possibilities seem allmost unlimited!