putting colour onto map

I imported a world map picture(bmp) using imread and show it using imshow. The map picture is currently black(value of black is zero). After I imported this, there is a uint8 file in the workspace that shows different numbers. for example, asia is 1, africa is 2 and so on and background is 0. I have the colorbar from 0 to 255 (black to white). I am supposed to put different shade of the colour bar onto the map from ascending order. For example, asia has the largest population so the colour is 255 for asia region. As the population decreases, the shade also decreases from 255 to 0 for different regions.

[KSSV]

Attach your image.

[Tantalic Oak]

This is the image