Painting of Transformer tank surface

What ever colour you like.

Pink is going to look a bit strange.

Some people suggsts aluminium paint..someothers suggests Smoke grey..which one is better for effective heat radiation and better cooling?

The fact that transformers have been painted any number of colors over the years, including black, various grays, green, etc., suggests that the color has minimal effect on the cooling of the transformer. The bigger consideration is air flow over radiator surfaces (fans or convection), radiator fin or tube configuration, forced oil flow (pumps), etc. Paint it to match the rest of your electrical equipment, or just pick a color you like!