patch-edid.rb

#!/usr/bin/ruby
# Create display override file to force Mac OS X to use RGB mode for Display
# see http://embdev.net/topic/284710

require 'base64'

data=`ioreg -l -d0 -w 0 -r -c AppleDisplay`

edids=data.scan(/IODisplayEDID.*?<([a-z0-9]+)>/i).flatten
vendorids=data.scan(/DisplayVendorID.*?([0-9]+)/i).flatten
productids=data.scan(/DisplayProductID.*?([0-9]+)/i).flatten

displays = []
edids.each_with_index do |edid, i|
    disp = { "edid_hex"=>edid, "vendorid"=>vendorids[i].to_i, "productid"=>productids[i].to_i }
    displays.push(disp)
end

# Process all displays
if displays.length > 1
    puts "Found %d displays!  You should only install the override file for the one which" % displays.length
    puts "is giving you problems.","\n"
elsif displays.length == 0
    puts "No display data found!  Are any external displays connected?"
    puts "\nNote: Apple Silicon (arm64) devices are currently unsupported, as the standard"
    puts "method of retrieving display information does not work."
end
displays.each do |disp|
    # Retrieve monitor model from EDID display descriptor
    i = disp["edid_hex"].index('000000fc00')
    if i.nil?
        monitor_name = "Display"
    else
        # The monitor name is stored in (up to) 13 bytes of text following 00 00 00 fc 00.
        # If the name is shorter than 13 bytes, it is terminated with a newline (0a) and then padded with spaces.
        monitor_name = [disp["edid_hex"][i + 10, 26].to_s].pack("H*")
        monitor_name.rstrip!            # remove trailing newline/spaces
    end

    puts "Found display '#{monitor_name}': vendor ID=#{disp["vendorid"]} (0x%x), product ID=#{disp["productid"]} (0x%x)" %
            [disp["vendorid"], disp["productid"]]
    puts "Raw EDID data:\n#{disp["edid_hex"]}"

    bytes=disp["edid_hex"].scan(/../).map{|x|Integer("0x#{x}")}.flatten

    puts "Setting color support to RGB 4:4:4 only"
    bytes[24] &= ~(0b11000)

    puts "Number of extension blocks: #{bytes[126]}"
    puts "removing extension block"
    bytes = bytes[0..127]
    bytes[126] = 0

    bytes[127] = (0x100-(bytes[0..126].reduce(:+) % 256)) % 256
    puts
    puts "Recalculated checksum: 0x%x" % bytes[127]
    puts "new EDID:\n#{bytes.map{|b|"%02X"%b}.join}"

    Dir.mkdir("DisplayVendorID-%x" % disp["vendorid"]) rescue nil
    filename = "DisplayVendorID-%x/DisplayProductID-%x" % [disp["vendorid"], disp["productid"]]
    puts "Output file: #{Dir.pwd}/#{filename}"
    f = File.open(filename, 'w')
    f.write '<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">'
    f.write "
<dict>
  <key>DisplayProductName</key>
  <string>#{monitor_name} - forced RGB mode (EDID override)</string>
  <key>IODisplayEDID</key>
  <data>#{Base64.encode64(bytes.pack('C*'))}</data>
  <key>DisplayVendorID</key>
  <integer>#{disp["vendorid"]}</integer>
  <key>DisplayProductID</key>
  <integer>#{disp["productid"]}</integer>
</dict>
</plist>"
    f.close
    puts "\n"
end             # displays.each

I have 2 external HDMI-to-usbc monitors. The override works and I can see it take effect in Settings > Displays, but when i rearrange the monitors in Display settings, one of the monitors gets blurry again. Anyone run into this?

Well I tried it in my M1 pro ti try to make de external monitor colors look better, and now my macbook screens says it is 1512 x 982 resolution, and if i try to increase it does not look good, also I lost some screen opions for the same macbook screen, and I just runned the script. Y can check in the imagems the light theme shows how it used to be and the dark how it is now.

@MikaelDDavidd This solution works on x86 based Macs. It's not meant for M1 based Macs, as they ignore the EDID override.

You can delete the override file you have created, reboot and it should be back to default.

If possible, try using an USB-C to DisplayPort port cable on the M1 Pro

Any way to make this work with BetterDisplay? It also works on Silicon-based Macs.