Try this... Remove the battery and try running it on just the charger cord alone. Does this stop the flashing and give you a solid white light?
If yes, then your battery is not charging, at least not when the laptop is on.
Put the battery back in and try turning off the laptop and see if the battery will charge then. If it will charge then (and no blinking color change) the problem may well be the charger cord. If it isn't putting out enough power to run the laptop and charge the battery at the same time this can happen. Then you would need to replace the cord.
If the problem still persists, no matter if trying to charge with the laptop on or off, then the battery is what will need replacing.