Hi Tint, welcome to the forum :)
Adjusting the Levels or Curves should not be changing the colour, just the tonality. If there is an apparent colour change, it means that the colour is actually there and the tonality change is just bringing it out. Compensate with a Hue/Saturation adjustment layer after Curves or Levels

This is a case where "adjustment layers" come in real handy ;)

:)
retrocity