Point transparency : difference between pch 16 and 19

The pch=19 is a circle and secondary plain circle. The pch=16 is only a plain circle. This is what to use for transparency.

plot(rep(1, 10) ,rep(1, 10), pch=19, cex=10, col=rgb(.1, .1, .1, 0.01), lwd=5)
plot(rep(1, 10) ,rep(1, 10), pch=16, cex=10, col=rgb(.1, .1, .1, 0.01), lwd=5)

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