Colour threshold from a mask

Hi people. I´m trying to do something and I can´t realize what I´m doing wrong. I have a mask, that has been done with a colour threshold macro from a RGB picture. I want to know the values of RGB channels used on that pictures to apply them in another picture. So, I obtained a selection from the mask, and whith this ROI I measured min and max values of RGB from the original pictures. When I use those min a max to colour threshold the original picture, I got a completely different selection/mask. I hope you can help me. Sorry for english!!!

Maybe the colour threshold macro was not set to work in RGB mode?
Also the colour threshold can be set to “pass” or “stop” the range of values in each channel.