heatmap with levelplot?

Hi,

How do I anchor z=0 to the white color in a levelplot so that
the color changes from cyan to magenta precisely as
z changes from negative to positive? Also is it easy to change
color scheme, say to blue/red as it's more dramatic? Is there a
better function for showing heatmap with a color bar?

Thanks in advance for any help, I've played with image,
heatmap and levelplot a little and haven't gotten very far.

Yuli Zhou