how do you change the colour of a mri brain scan to a solid black or white

having trouble finding a function that changes the colour of a dicom image of the brain to a solid black or white

[Image Analyst]

Do you mean an RGB color, or a gray scale intensity "color"?

[Walter Roberson]

Or do you mean thresholding? If so then is the original image RGB or greyscale ?

[Doug Hull]

Do you just want to change the colormap?