Random use with all LEDs on the same color

Hi,
I'm trying to create a bash script that turns to a random color my ambilight, for a random period between 0 & 2 seconds, using hyperion-remote.

Unfortunately, when I use for example:
hyperion-remote -p 49 -d 2000 -R 255 -G 5 -B 25
or
hyperion-remote -p 49 -d 2000 -R 255 5 25
or
hyperion-remote -p 49 -d 2000 -R 255 -G 005 -B 025
or
hyperion-remote -p 49 -d 2000 -R255 -G5 -B25
I receive this error message:
-R: Argument 255 can not be parsed to 3 integer values

This works:
hyperion-remote -p 49 -d 2000 -c 1189ff
but I don't know how to obtain a random variable between 0 and FFFFFF...that's why I try to use -R -G -B because I found how to generate random number:
let "red = $[ ( $RANDOM % 255 ) + 1 ]"
let "green = $[ ( $RANDOM % 255 ) + 1 ]"
let "blue = $[ ( $RANDOM % 255 ) + 1 ]"

Any idea please?