plot(1:20, y=rep(0,20), col = 1:20, cex = 2, pch = 20 )

• Hexadecimal notation is used (0 ~ 9, A ~ F)
• Basically Red, Green and Blue colors are used and they are represented by two hexadecimal characters. That is, each basic color has 256 levels (#rrggbb)
• \(256 \times 256 \times 256 = 2^24\) colors can be displayed: 24 bit colors.
• Moreoever, 256 opacity levels are added into 24bit colors such that 32 bit rgb color system is completed. (##rrggbbaa)

• Basic colors

head(colors())

## [1] "white"         "aliceblue"     "antiquewhite"  "antiquewhite1"
## [5] "antiquewhite2" "antiquewhite3"

tail(colors())

## [1] "yellow"      "yellow1"     "yellow2"     "yellow3"     "yellow4"    
## [6] "yellowgreen"

    mycol = colors()
    plot(1:80, y=rep(1,80), col = mycol[1:80], cex = 2, pch = 20, 
         ylim = c(0,1) )
    points(1:80, y=rep(0.5,80), col = mycol[81:160], cex = 2, pch = 20 )
    points(1:80, y=rep(0,80), col = mycol[161:240], cex = 2, pch = 20 )

mycol = colors()
image(matrix(1:25^2,25,25), col = mycol)

• rgb(red, green, blue, maxColorValue, alpha)
• red, green, blue : by default 0 ~ 1.
• 256 scale (0-255) is available by setting maxColorValue = 255.
• alpha : opacity

rgb(10, 4, 23, maxColorValue = 255, alpha = 10)

## [1] "#0A04170A"

col2rgb('lightblue')

##       [,1]
## red    173
## green  216
## blue   230

• 
• colors are displayed on a cone.
• The outter colors has higher saturations.
• As going up, the brightness is increasing.

• hcl(h, c, l, alpha)
• h: colors, c: saturation, l: brightness, alpha: opacity
• h\(\in [0,360]\): 0~120(red), 120~240(green), 240~360(blue)
• l \(\in [0, 100]\), alpha \(\in [0,1]\)
• range of c depends on the value of h and l.

hcl(h = 0, c = 35, l = 85, alpha = 0.1)

## [1] "#FFC5D01A"

• hsv(h, s, v, alpha)
• h: color, s: satulation, v: brightness, alpha: opacity
• h, s, v, alpha \(\in [0,1]\)

hsv(0.3, 0.5, 0.1, alpha = 0.4)

## [1] "#0F1A0D66"

• cm.colors, topo.colors, terrain.colors, heat.colors, rainbow
• cm, topo, terrain, heat : n (number of colors), alpha (opacity)

heat.colors(4, alpha = 1)

## [1] "#FF0000FF" "#FF8000FF" "#FFFF00FF" "#FFFF80FF"

topo.colors(4, alpha = 1)

## [1] "#4C00FFFF" "#00E5FFFF" "#00FF4DFF" "#FFFF00FF"

x <- 10*(1:nrow(volcano))
y <- 10*(1:ncol(volcano))
image(x, y, volcano, col = heat.colors(20, alpha = 1), axes = FALSE)
contour(x, y, volcano, levels = seq(90, 200, by = 5),
        add = TRUE, col = 'white')

x <- 10*(1:nrow(volcano))
y <- 10*(1:ncol(volcano))
image(x, y, volcano, col = topo.colors(20, alpha = 1), axes = FALSE)
contour(x, y, volcano, levels = seq(90, 200, by = 5),
        add = TRUE, col = 'white')

• rainbow colors adopts hsv color system.
• n (number of colors), s (saturation), v (brightness), start (staring value of h), end (ending value of h), alpha (opacity)
• the range of start, end: 0 ~ 1

rainbow(5, s = 0.4, v = 0.3, start = 0, end = 0.05, alpha = 1)

## [1] "#4D2E2EFF" "#4D302EFF" "#4D322EFF" "#4D352EFF" "#4D372EFF"

• Form this package we can define various palettes available in R
• sequential palettes : Blues, BuGn, BuPu, …, YlOrBr, YlOrRd

library(RColorBrewer)
brewer.pal(4, 'Blues')

## [1] "#EFF3FF" "#BDD7E7" "#6BAED6" "#2171B5"

x <- 10*(1:nrow(volcano))
y <- 10*(1:ncol(volcano))
image(x, y, volcano, col = brewer.pal(9, 'Blues'), axes = FALSE)

• Diverging palettes : BrBG, PiYG, .., RdYlGn, Spectral
• Middle colors are bright and the starting and ending colors are dark.

library(RColorBrewer)
brewer.pal(4, 'BrBG')

## [1] "#A6611A" "#DFC27D" "#80CDC1" "#018571"

• display.brewer.all()
• This function shows palettes available in RColorBrewer package.

library(RColorBrewer)
display.brewer.all()

• Color palette based on hcl, hsv color system.
• diverge_hcv, diverge_hsl, terrain_hcl, sequential_hcl, rainbow_hcl, …

library(colorspace)

## Warning: package 'colorspace' was built under R version 3.4.1

diverge_hcl(7, h = c(246, 40), c = 96, l = c(65, 90))

## [1] "#1FA4FF" "#97BFF3" "#CAD6E9" "#E2E2E2" "#E7D1C5" "#E9B18B" "#E28912"

library(colorspace)
pal = choose_palette()

• 
• Interactive tool to make color palettes
• options are referred in RColorBrewer.

• 
• Default automatically chooses color, saturation, brightness.
• There are various options for hcl or hsv

• 
• Check the examples.
•