imagesc will use the colormap of the figure, so if you want to use a different color scheme for scatter, calculate out the rgb values to use. See the sample code to see how 2 color schemes can be used:
A = rand(100,200); % the image to be presented...
HotClr = hot; %Mx3 rgb matrix for hot color scheme (for imagesc)
CoolClr = cool; %Mx3 rgb matrix for cool color scheme (for scatter)
imagesc(A) %will autoscale image according to FIGURE's ColorMap
colormap(gcf, HotClr); %setting figure colormap to hot color scheme
hold on
CoolIdx = ceil(linspace(1, size(CoolClr, 1), 100)); %find index of the different color map
scatter(1:100,1:100,30,CoolClr(CoolIdx,:),'filled'); %use the RGB values per dot instead of figure colormap index.
hold off
