如何绘制颜色编码密度散点图的图例？

Question

我正在使用以下代码制作带有颜色编码密度的散点图：

d1 = densCols(newData_cut, 
          colramp = colorRampPalette(c("navy 
         blue","yellow","firebrick","firebrick"), 
                                     space = "Lab"))

ggplot(newData_cut) + 
   geom_point(aes(x=green, y= blue, col = d1), size = 1) +
   xlim(0, 0.4)+
   ylim(0,2)

但是当我得到图像时，它看起来像这样：

有人可以帮助我用一个代表点数/密度的颜色绘制一个合适的图例吗？

> dput(head(newData_cut))
structure(list(green = c(0, 0.229804, 0, 0, 0, 0), blue = c(0.080264, 
0.204474, 0.04059, 0.040284, 0.042421, 0.041505), width = c(1317, 
4529, 1, 10, 23, 5)), .Names = c("green", "blue", "width"), row.names = 
c(NA, 
6L), class = "data.frame")