To get filled curves between y=0 axis and plot using b2r

My code runs: close all; clear all; b = -5 + (5+5)*rand(80,1) a=[1:1:80]; plot(a,b,'k'); colorbar colormap(b2r(-5,5))

This generates the attached plot. I need the plots filled up in accordance to gradient. Any help shall be highly appreciated. Also I shall like to know how can I fill positives with red and negatives with blue.