Command in R: “colorRampPaletteAlpha” code that can be helpful when creating a color palette.

#from Github source
install.packages("devtools")
devtools::source_url("https://raw.githubusercontent.com/mylesmharrison/colorRampPaletteAlpha/master/colorRampPaletteAlpha.R")

#Loading the scales package
library("scales")

#Get color code for specified transparency and color:addalpha command
#Alpha value:alpha option
show_col(addalpha("red", alpha = 0.1))
###code#####
function(colors, alpha=1.0) {
  r <- col2rgb(colors, alpha=T)
  # Apply alpha
  r[4,] <- alpha*255
  r <- r/255.0
  return(rgb(r[1,], r[2,], r[3,], r[4,]))
}

#Create a gradient palette with the specified color:colorRampPaletteAlpha command
#Specify completion method:interpolate option;"spline","linear"
show_col(colorRampPaletteAlpha(c("red", "yellow", "blue"), n = 20, interpolate = "spline"))
###code#####
function(colors, n=32, interpolate='linear') {
  # Create the color ramp normally
  cr <- colorRampPalette(colors, interpolate=interpolate)(n)
  # Find the alpha channel
  a <- col2rgb(colors, alpha=T)[4,]
  # Interpolate
  if (interpolate=='linear') {
    l <- approx(a, n=n)
  } else {
    l <- spline(a, n=n)
  }
  l$y[l$y < 255] <- 255 # Clamp if spline is < 255
  cr <- addalpha(cr, l$y/255.0)
  return(cr)
}