Colour gradient, with midpoint
> dsub <- subset(diamonds, x > 5 & x < 6 & y > 5 & y < 6) > (d <- qplot(x, y, data=dsub, colour=x-y))> > d + scale_colour_gradient()
> # Change scale name > d + scale_colour_gradient(expression(x - y))
> d + scale_colour_gradient("Difference\nbetween\nwidth and\nheight")
> > # Change limits and colours > d + scale_colour_gradient(limits=c(-0.2, 0.2))
> d + scale_colour_gradient(mid="black", high="yellow", low="yellow")
> > # You can also use a non-zero midpoint > (d <- qplot(carat, price, data=diamonds, colour=price/carat))
> d + scale_colour_gradient(midpoint=mean(diamonds$price / diamonds$carat), high="darkgreen", mid="yellow")
> > # Fill gradients work much the same way