There's a programmatic way of doing it, but this is the GUI point and click method; Right click on the colorbar -> Open Colormap Editor The colorbar will appear as a horizontal stripe with little flags below it. Double click the green flag. This brings up a color selection window, pick white and go OK.
To do this automatically in the future you can save the colormap with;
myColormap = colormap;
save('colormapsavefile.mat','myColormap');
To apply;
load('colormapsavefile.mat');
colormap(myColormap);
With some tweaking you can set the default colormap using this method and the startup.m file.
