How to show different colours as different regions (by assigning different grey level values to each region corresponding to a particular colour)

Need help

Answer 1

[Walter Roberson]

Use a labeled array and ind2rgb()

[Arshad Ali]

I am new at matlab don't have any idea how to use

[Walter Roberson]

Start with (for example) http://blogs.mathworks.com/steve/2006/11/17/labeling-labeled-objects/ . Once you have the L matrix, pass it to ind2rgb() along with a colormap; see https://www.mathworks.com/help/matlab/ref/ind2rgb.html