Combining two plots from bayesplot

[David Kaplan]

Greetings all,

I'm having trouble combining two plots from "bayesplot".  The code is 

color_scheme_set("gray")
prior_rep_correct <- as.matrix(Correctpriorpred,pars="prior_rep_correct")
plot_correct <- ppd_dens_overlay(prior_rep_correct[1:50,])
plot_correct + lims(x=c(0,800))

and

color_scheme_set("darkgray")
prior_rep_incorrect <- as.matrix(Incorrectpriorpred,pars="prior_rep_incorrect")
plot_incorrect <- ppd_dens_overlay(prior_rep_incorrect[1:50,])
plot_incorrect + lims(x=c(0,800)) + ylab("Prior Predictive Density")

Thanks in advance

David