colour.rb

require "stringio"
substr1 = encode_str [255, 0, 0, 1, "h"]
substr2 = encode_str [0, 13, 24, 4, "ello"]
str = StringIO.new(substr1 + substr2)
read_directive(str)

def encode_str(str_tuple)
  [128396, str_tuple].flatten.pack("UC4a*")
end

def read_directive(str)
  return if str.eof?
  val = str.read(4).unpack("U")
  match = [128396]
  case val
  when match
    puts "This is a string colouring"
    puts "Red value: #{str.read(1).unpack("C")}"
    puts "Green value: #{str.read(1).unpack("C")}"
    puts "Blue value: #{str.read(1).unpack("C")}"
    length = str.read(1).unpack("C").first
    puts "Length of string #{length}"
    puts "String is: #{str.read(length)}"
    read_directive(str)
  else
    "fail: #{val} #{match}"
  end
end

output

2.1.2 :408 > substr1 = encode_str [255, 0, 0, 1, "h"]
 => "\xF0\x9F\x96\x8C\xFF\x00\x00\x01h"
2.1.2 :409 > substr2 = encode_str [0, 13, 24, 4, "ello"]
 => "\xF0\x9F\x96\x8C\x00\r\x18\x04ello"
2.1.2 :410 > str = StringIO.new(substr1 + substr2)
 => #<StringIO:0x007fe2b11bd960>
2.1.2 :411 > read_directive(str)
This is a string colouring
Red value: [255]
Green value: [0]
Blue value: [0]
Length of string 1
String is: h
This is a string colouring
Red value: [0]
Green value: [13]
Blue value: [24]
Length of string 4
String is: ello
 => nil