How to edit pixels subsequently after using imagesc??

Hi everyone. I'm using imagesc to map some data in color maps. I managed to get the data by a handle to save every single picture/figure. But now I would like to replace some pixels, that are out of range (I defindes a range by clims), by white or black. I exactly know what pixels, so I know the location. But I don't get the pixels to edit them out of the figure. I would like to highlight so to speak all pixels, that are out of the defined range. It would be perfect, if you can help me. Greetings