Yellow fins, yes, blue fins... Not yet. Bettas don't actually come in all different colours, txbettaowner.
Quoted from bettysplendens-
"The characteristic thick, silvery/white metallic layer on the body istypically found red, yellow, orange, white and black "dragons". In caseof red, yellow and orange "dragons" this layer can be observed in bothlight- and darkbodied fish.
Interestingly, so far this characteristic silvery/white metallic layerhas not been observed in darkbodied bettas with a classical iridescentcolor (steel blue, turquoise or royal blue) of the body and finnage.The picture shows an imaginary example of what the authors mean withthis.
In case of a dark bodied "dragons" with a classical iridescent base,the silvery/white appearance seems to be masked although based onmacroscopic observation (with the naked eye) their scaling definitelyseems to differ from a regular metallic fish by being more solid. Therehave been reports of red and black dragons with a blueish shine ontheir scaling but so far no real blue "dragons" with this typicalthick, silvery/white scaling have been developed. It would beinteresting to find out whether it is possible to obtain a the thick,silvery/white metallic layer back after crossing a blue or copper"dragon" as depicted above to a red, yellow, orange or black betta."