In photoshop CS using thecolor replacement tool, I always get a 'blend' of the 2 rather than a replacement

I follow all the tutorials perfectly...could my color settings be off? if so what should they be? OR am I missing something basic? I choose color replacement tool, click on color picker, choose a color...settings to color, once, contigious and tolerance at 30% but I always get a blend of the color that was there and the new color. HELP!