Color Replacement Tool does not replace colour correctly

Hey there. I am having some difficulty with the colour replacement tool. I am trying to change a white-ish area of a photograph to brown. I have selected the correct shade of brown as my foreground colour, but when I start the replacement, I get an unattractive shade of pink. If I try other random colours from the colour picker, I get the same weird pink. I am not editing a mask, and it doesn't seem to matter whether I am on a layer or on my background. I have tried this with other photos, and the effects are sometimes more bizarre - pinks turn grey, greens turn brown (yay - one brown!). I have tried different modes (color is the one I want), different sampling (Contiguous makes most sense in this case). There have been occasions in the past where I have been very successful with this tool, but I cannot understand why this seems to be a rare and random occurrance. Any help?

Computer: Mac Pro, 4GB RAM, Mac OS 10.4.11
Image: 16 bit RGB, PSD format

The Color Replacement brush is a very difficult tool to use. The problem is that it only paints with one component of your sampled "color" at a time,

To turn a whitish area to a deep brown, you may need to sample the "brown" and then paint with Luminosity, Color, Saturation and Hue in turn to build up the color to match your chosen Brown.

Working on a duplicate overlying Layer and setting that finally to Color mode and appropriate opacity might help you.