Marvel Girl.
After a falling out with her father Cyclops over his relationship with Emma Frost, Rachel changed her name from Summers to Grey and adopted a modernized version of her mother's original graduated X-Men costume.
Rachel also started using her mother's former codename as well, and it was during this period as Marvel Girl that she also began to project a new dark energy form when using her powers, with only her eye left aglow from the Phoenix brand.