To change the colour selectively, click the Hue, Saturation or Lightness button to have the vertical gradient select that option only, so that if you just want to change the Hue, click on that button.
Add a tint or haze by overlaying a solid colour. Use a blending mode of Soft Light for a tint and Screen for a haze. Adjust the Opacity to get the level of effect. Note dark and light colours have different effects. You can add the effect and then open the Colour Picker again and alter the colours in real time. Ref.