From grayscale to monochrome in a given selected color

I have grayscale images that I would need to convert into monochrome for different colors; i.e. one image into red monochrome, another image into green monochrome, etc

Answer 1

[Walter Roberson]

   mono = double( im2gray(YourImage) > 0.5 );
   monoRed = cat(3, mono, zeros(size(mono)), zeros(size(mono)) );