This should do. Valid input is assumed.

Code:
alias tohex return $+($base($1,10,16,2),$base($2,10,16,2),$base($3,10,16,2))

alias torgb {
  tokenize 44 $rgb($regsubex($1,/([\da-f]{6})/i,$base(\1,16,10)))
  return $3 $+ , $+ $2 $+ , $+ $1
}