The most likely cause is light exposure to the film, either from a camera light leak or from opening the back before the film was fully rewound into the cassette. A straight bright band and heavy color shift are consistent with stray light hitting the film.

On the Minolta X-700, the back should stay closed except when loading or removing a fully rewound roll. If any film was still out of the cassette when the back was opened, that could easily ruin frames or the rest of the roll.

What to do:

• Check the camera back, seals, hinges, and latch for gaps or damage.
• Review the X-700 loading and rewinding procedure in the manual.
• Load film in subdued light.
• When rewinding, make sure the film is fully back in the cassette before opening the camera.

Since only a few frames were salvageable, accidental opening during rewind is a strong possibility, but worn seals or back damage could also cause it.