[BioC] heatmap.2

[Paolo Kunderfranco]

Dear All,
I am struggling with heatmap to plot RNA-seq data,
my dataset values range from -8 to 10(logFC), I would like to use some
colours that can display differencies in all ranges,
I tried with

heatmap.2(a,col=greenred(75))

but somehow values from 8 to 9 are stack together and I cannot
appreciate differencies,
Attached is somehow what I would like,
Thanks,
Paolo