Apply a hue/saturation layer with high saturation, Alternately, you can paint the colors on using a Color blending mode, which will preserve the luminosity detail but replace your color.

It would help to know how you are applying the colors. Since I've never found a reason to do this, I haven't tried myself, but I understand the theory.

They had chained him down to things that are, and had then explained the workings of those things till mystery had gone out of the world....And when he had failed to find [wonder and mystery] in things whose laws are known and measurable, they told him he lacked imagination, and was immature because he preferred dream-illusions to the illusions of our physical creation.
      -- HP Lovecraft, The Silver Key