'Colour offset'.
That's your chappie, Martin is correct with the contrast details, aswell.
You want to reduce the 'colour offset' in the fractal(if you're using only 'high colour', raise it if you're using 'low colour', it balances the high/low distribution. If you're using both high/low colours, it describes how dominant each colour is.) to make less coverage of a certain surface, keep your surface layer at '1' coverage and reduce the colour offset in the fractal to reduce the amount of 'colour-spread' being applied.
The power fractal can also wash your dishes, if you ask it nicely, it can do anything, it's a real smart arse.

Just negate the offset to reduce high colour distribution, raise it to reduce low colour distribution. Keep your parent surface layer at coverage='1'.