[R] definition of colorpalette

[Daniel Stepputtis R]

Dear group,

I have recognized a strange behaviour of palette(). I tried to find any 
explanation but failed so far (or even didnt understood the idea behind 
- what is most probable).

My original plan was to define a palette, save it in a variable and use 
it later for an image-plot. One reason why I tried to store the palette 
in a variable was, because I wanted to change individual values (e.g. 
the first value to gray).

Interestingly, the palette is not defined correctly in the first run, 
but in the second run.
Simple example:

 >rm(list=ls())
 > a <- palette(rainbow(6))
 > a
  [1] "red"     "#FF4C00" "#FF9900" "#FFE500" "#CCFF00" "#80FF00" 
"#33FF00" "#00FF19" "#00FF66" "#00FFB2" "cyan"    "#00B3FF" "#0066FF" 
"#0019FF" "#3300FF" "#8000FF" "#CC00FF"
[18] "#FF00E6" "#FF0099" "#FF004D"
 > a <- palette(rainbow(6))
 > a
[1] "red"     "yellow"  "green"   "cyan"    "blue"    "magenta"

###################
Interestingly, this works at the first time
 > palette(rainbow(20))     # six color rainbow
 > plot(rnorm(20),col=1:20)

as well as
 > palette(rainbow(6))
 > a <- palette()
 > a
[1] "red"     "yellow"  "green"   "cyan"    "blue"    "magenta"

So, it seems to be that first a palette has to be defined (or set as to 
be used) and then the vector can be assigned to a variable. I dont 
understand why.

Thank you in advance for your help and explanation.

Daniel