Add alpha value to lattice xyplot panel function

Question

I want to assign two alpha values in xyplot panel function: points with alpha= 0.3 and lines with alpha=1. Here is an example:

library(lattice)
library(sp)
data(meuse)

xyplot(elev~ copper,data=meuse,groups=factor(soil),grid = TRUE,scales=list(tck=c(1,0), x=list(cex=1.1), y=list(cex=1.1)),
       auto.key = list(space = 'right',text=c("1", "2", "3")),
       par.settings = list(superpose.symbol = list(pch =20, cex = 1,
                                                   col = c("#006837", "#41ab5d","#fd8d3c"))),
      type = c("p", "smooth"),col.line =c("#006837", "#41ab5d","#fd8d3c"),lwd = 5,
      panel = function(x, ...) {
                panel.xyplot(x, ..., alpha = 0.3)
                panel.lines(x, ...,  alpha = 1)
            })

Answer 1

An hex value can be read as "#rrggbbaa" where r = red, g = green, b = blue and a = alpha. Since the decimal values for opacity range from 0 to 255, in a traditional rgb notation; the value for 30% opacity would be round((256/100)*30) = 77, and hexadecimal value for this is 4d (there is a list with some examples here for reference and a conversion table dec - hex can be found here).

Therefore, you just need to add 4d at the end of your hex code for the points color as:

col = c("#0068374d", "#41ab5d4d","#fd8d3c4d")

and remove

panel = function(x, ...) {
            panel.xyplot(x, ..., alpha = 0.3)
            panel.lines(x, ...,  alpha = 1)
        }