How to do a grip map?

Hi everyone, i'm trying to create two grid maps like this one. One has 256*45 and the other has 282*45. In fact, a friend of mine provided me a Matlab script that creates this type of figures, but I'm not totally satisfied because of the shade of black on the bottom of the map which I selected in the picture attached . In short, I'm trying to convert a matrix of numbers (only containing the values 1,2 or 3) in a colourmap corresponding a colour to each number. Is there any better code that i can use to do this?