you've got to plug in your texture (file, ramp, fractel, whatever) to the value input. set old min to 0 0 0 and old max to 1 1 1 (if you now the exact value range you can type it in)

with min and max (not old min and max) you can now specify a new range. middle mouse drag the set range node into the color input of the shade you connected your model to.

look in the viewer to get it the way you want it.

greets