Use paint bucket to change only one color

Hi,

I am having trouble with using paint bucket tool to fill just one area. 

What is happening it is mixing in with other images on the page with different tones of the same color. 

I have seen on the web a few years ago that you can constrain the fill option to a hex color only, but cannot seem to find the

right information.

I have inserted rectangles on the images of a different color to see if that would work but to no avail.

Any help would be much appreciated.

Thanks,

Steven Williams