colorRamp2(x, alpha = TRUE, thresholds = NULL)

# Creating a function for 2 colors
myf <- colorRamp2(c("black", "steelblue"))
f   <- colorRamp(c("black", "steelblue"))

plot.new()
plot.window(xlim = c(0,2), ylim = c(1, 11))

# These should be the same colors
rect(
  xleft   = 0,
  xright  = 1,
  ybottom = 1:10,
  ytop    = 2:11,
  col = rgb(myf((1:10)/10), maxColorValue = 255)
  )
rect(
  xleft   = 1,
  xright  = 2,
  ybottom = 1:10,
  ytop    = 2:11,
  col = rgb(f((1:10)/10), maxColorValue = 255)
)

# Another example setting different thresholds
myf  <- colorRamp2(c("black", "steelblue"))
myf2 <- colorRamp2(c("black", "steelblue"), thresholds=c(0, .7))

plot.new()
plot.window(xlim = c(0,2), ylim = c(1, 11))

# These should be the same colors
rect(
  xleft   = 0,
  xright  = 1,
  ybottom = 1:10,
  ytop    = 2:11,
  col = rgb(myf((1:10)/10), maxColorValue = 255)
  )
rect(
  xleft   = 1,
  xright  = 2,
  ybottom = 1:10,
  ytop    = 2:11,
  col = rgb(myf2((1:10)/10), maxColorValue = 255)
)