[BioC] heatmap.2 coloring question

[Srinivas Iyyer]

Dear group, 
I am using heatmap.2 for heatmaps. 

heatmap.2(res1,cexRow = 0.28,cexCol=0.28
,col=rev(heat.colors(16)),keysize=1,na.color=par("bg"),densadj
= 0.25,Colv=FALSE)



I want to have a color key starting from blue to
yellow through white.

Say -7 is my min value and +4 is my max value. 

Values around 0 should be totally white. 

what kind of trick can do that for me. I will be very
happy if I can do that. 

Any suggestions, please. 
thank you. 
srini