The “GLCOL” option requires ROOT 5.30 or newer.
See also: http://root.cern.ch/root/html/TGLHistPainter.html and http://root.cern.ch/root/html/THistPainter.html
In general, you can define your own contour levels and palette, see for example: [url]TH2 Drawn with "colz" option - colors and range