I can't remember the shader you refer to, but the root colour would normally be white as you say. Possibly I was doing a dark hair with coloured tips.

Ihave just looked at a set-up as you describe and with a cloud node the bottom value had to be set to zero and the gain to more than .9 to provide enough contrast to drive all four steps in the colour ramp.

Putting a noise node onto the ramp colours darkens them considerably unless you increase the min value considerably (this is the main reason for difficulty producing a blonde hair)