Use density and fields::colorbar.plot
require(fields)
plot(1:10, rep(1,10), ylim=c(0,10))
colorbar.plot( 2, 4, 800*density(rgamma(100, shape=2))$y)
colorbar.plot( 2, 5, 800*density(rexp(100))$y)
colorbar.plot( 2, 6, 800*density(rnorm(100))$y)
colorbar.plot( 2, 7, 800*density(rlnorm(100))$y)
text(6,4, "Gamma")
text(6,5, "Exponential")
text(6,6, "Normal")
text(6,7, "LogNormal")