You have to Right Click chart > select color tab -> Set Image Option -> Select Image
This is static setting . Please refer jpg I have attached.
Hope this hep you.
jpg.bmp 2.3 MB
these map are extension not static chart...
if i rght clik the map,its properties are like --see attachments
ist show open layer property
n 2nd shows google map property..
In there map i am calculating sum(population) in both mapp....
when population is extrme high its show by dark color,then little bit light color then mro light...
This u can see in heat wise openlayer.png