How to change the colors in colormap function

I have the expression below to plot the power with respect to x and y position. The colors vary based on the power level. I plotted the power using the expression below however the colors are gray, black etc. I need the colors to be red indicating high power, orange, blue, yellow, as the power goes from high to low.

cmap = 0:1/256:1; 
cmap = [ cmap; cmap; cmap ]';
imagesc(data.power); 
axis equal; 
axis xy; 
colormap( cmap );

Answer 1

[Image Analyst]

You can try one of the many built-in colormaps such as hsv, jet, parula, etc.

cmap = jet(256);
colormap(cmap);
colorbar;

[Steven Lord]

And if none of the colormaps included in MATLAB do exactly what you want, you can start with the one that's closest and tweak it using COLORMAPEDITOR.

Answer 2

[Stephen23]

Identical R, G and B values gives gray, and this is what you are defining in your variable cmap.

If you want colors then why not simply read the colormap documentation and use one of the inbuilt colormaps. The documentation has working examples and figures showing all the inbuilt colormaps. Or pick any of the very attractive colormaps that are available on MATALB File Exchange:

http://www.mathworks.com/matlabcentral/fileexchange/43700-cubehelix-colormaps--beautiful--distinct--versatile-

http://www.mathworks.com/matlabcentral/fileexchange/45208-colorbrewer--attractive-and-distinctive-colormaps

http://www.mathworks.com/matlabcentral/fileexchange/51986-perceptually-uniform-colormaps