Male betta fish are known for their long, flowing fins that deepen in color when they feel territorial. Female bettas are less showy; they have shorter, rounded fins and muted colors. Females, born nearly white, change colors throughout their lives. While they do not necessarily change colors more than male members of the species, they may change colors just as frequently.
Change of Life, Change of Color
For the first 6 to 8 months of life, a female betta's color will gradually deepen as she approaches sexual maturity. When she is ready to breed, her coloration will deepen; a dark vertical band will extend the length of her body, and her belly will swell with eggs. Her colors will shine brightest when she's enjoying her surroundings and will pale if she becomes injured or if the temperature or water chemistry of her tank falls outside optimal levels. As she reaches old age, at 5 to 7 years, her colors will begin to fade, and her back will take on a bent and weary look.