Try concatenating colormaps, like this. Below I'm using my cmocean colormaps, which are available on File Exchange, but you can concatenate any RGB arrays.
% Some data
Z = abs(peaks(500));
Z = 100*Z/max(Z(:)); % scaled 0 to 100
figure
imagesc(Z)
cb = colorbar;
% Two colormaps:
col1 = cmocean('amp',6); % 6 shades of red
col2 = parula(95); % 95 shades of parula
% Concatenate colormaps:
col = cat(1,col1,col2);
colormap(col)
