Hello,
 
I can't seem to add transparency to any color ramp I create using colorRampPalette(). Can someone tell me if it is possible to create transparent colour ramps?
 
I am attempting to map shaded relief under elevation data. I know I can use the terrain.colors() with the alpha option, but I would prefer to create my own colour ramp using more vibrant colours. 
 
My most recent attempt at doing this involved generating multiple rgb colours with transparency (alpha = 0.5) and then combining these colours using colorRampPalette(). I am able to use the resulting colour ramp, but it has no transparency.
 
 # Make terrain colour ramp
      rgb7 <- rgb(red=0, green=255, blue=77, alpha = 0.5, maxColorValue = 255)
      rgb8 <- rgb(red=26, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
      rgb9 <- rgb(red=128, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
      rgb10 <- rgb(red=230, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
      rgb11 <- rgb(red=255, green=255, blue=0, alpha = 0.5, maxColorValue = 255)
      rgb12 <- rgb(red=255, green=229, blue=60, alpha = 0.5, maxColorValue = 255)
      rgb13 <- rgb(red=255, green=219, blue=119, alpha = 0.5, maxColorValue = 255)
      rgb14 <- rgb(red=255, green=224, blue=178, alpha = 0.5, maxColorValue = 255)
      rgb15 <- rgb(red=255, green=255, blue=255, alpha = 0.5, maxColorValue = 255)
      terraincolours <- colorRampPalette(c(rgb7, rgb8, rgb9, rgb10, rgb11, rgb12, rgb13, rgb14, rgb15))
 

# Plot map
      image(terrain, col = shadecolours(512), axes = TRUE) # plots the shaded relief
      #image(dem, col = terrain.colors(512, alpha = 0.5), add = TRUE) # this option works, but I don't like the colours in the terrain.colors pallet.
      image(dem, col = terraincolours(512), add = TRUE) # draws the elevation data with no transparancy and it won't accept an alpha value 
Thank you,
 
James

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