Something like this:
% Assuming your grayscale image is: d in double format
grayscaleIM(:,:,3) = (d-min(d(:)))/(max(d(:))-min(d(:)));
grayscaleIM(:,:,2) = (d-min(d(:)))/(max(d(:))-min(d(:)));
grayscaleIM(:,:,1) = (d-min(d(:)))/(max(d(:))-min(d(:)));
figure
colormap(jet)
imagesc(x,y,grayscaleIM)
hold on
scatter(X,Y,23,V,'filled')
colorbar
Perhaps you have your data in some other formats but you can easily produce an RGB-image that only shows gray-scale or a binary black-white image regardless of what colourmap you use. Then the scatter-plot will work with the current colormap, as should the colorbar.
HTH
