As you mention imagesc, I will presume that you want the minimum value to map to the first color in the colormap, and the max value to map to the last color in the colormap.
cmap = jet(107); %define colormap and number of entries, max 256
mg = mat2gray(ValueArray);
mgint = im2uint8(mg);
rgb = ind2rgb(mgint, cmap);
hexstr = reshape(cellstr(num2str(reshape(rgb, [], 3), '%02x')), size(rgb,1), size(rgb,2));
The result will be a cell array with the same number of rows and columns as the image, and each entry will be a character vector length 6 of hex digits, in the order R, G, B
