Multiple Ploting Colors

I'm trying to use multiple plotting colors in my code. My first "ifelse"

want. However, now I want anything less than -4.5 to be green and the rest

argument but can only use one. How could I go about getting separate colors

than -4.5?

plot(three, type="h", col=ifelse(three > 4.5, "red", "black"), xlim=c(0,500),

     xlab="Chromosome", ylab="Z-Score", font.lab=2, font=2, main="Upregulated

Thanks in advance,

Patrick

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