# Re: [R] color scale mapped to B/W

From: Achim Zeileis <Achim.Zeileis_at_wu-wien.ac.at>
Date: Sat, 07 Jun 2008 01:23:21 +0200 (CEST)

> In an R graphic, I'm using
>
> cond.col <- c("green", "yellow", "red")
> to represent a quantitative variable, where green means 'OK', yellow
> represents 'warning'
> and red represents 'danger'. Using these particular color names, in B/W, red
> is darkest
> and yellow is lightest. I'd like to find color designations to replace
> yellow and green so
> that when printed in B/W, the yellowish color appears darker than the
> greenish one.
>
> Is there some tool/code I can use to find these? i.e., something to display a
> grid
> of color swatches with color codes/names I can look at in color and B/W to
> decide?

You could look at colors in HCL (i.e., polar LUV). For example, you could choose a dark red HCL = (0, 90, 40) and a light green (120, 70, 90) and a yellow somewhere in between.

To emulate what happens when you print that out, you just set the chroma to zero.

There are some functions helpful for that in "vcd", you could do

library("vcd")

## select colors from dark red to light green    c1 <- heat_hcl(3, h = c(0, 120), c = c(90, 70), l = c(40, 90), power=1.7)    c2 <- heat_hcl(3, h = c(0, 120), c = 0, l = c(40, 90), power=1.7)

## visualize in color and grayscale emulation

```   plot(-1, -1, xlim = c(0, 1), ylim = c(0, 2), axes = FALSE)
rect(0:2/3, 0, 1:3/3, 1, col = c1, border = "transparent")
rect(0:2/3, 1, 1:3/3, 2, col = c2, border = "transparent")

```

The ideas underlying this color choice are described in this report we've written together with Kurt and Paul:

hth,
Z

> thanks,
>
>
> --
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> Dept.
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