datdat = randn(5,10);
regregnames = {'A', 'B', 'C', 'D', 'E'};
colors = cell(1,size(datdat,2));
for i=1:size(datdat,2)
    colors{i} = [1,1,1];
end
colors{3} = [1,0,0];
s.Labels = arrayfun(@num2str, 1:size(datdat,2), 'UniformOutput', false);
s.Colors = colors;
clscls = clustergram(datdat, 'RowLabels', regregnames, 'ColumnLabels', s.Labels, 'ColumnLabelsColor', s, 'LabelsWithMarkers', true);