Quick guide to enable correct color mode and 125% scaling on external Dell 4K (2650 x 1440) monitors with your MacBook. (Instructions for Windows and OSX). This gives you a smoothly scaled external monitor experience which keeps UI elements approximately the same ‘size’ as you drag them between the Retina and external display. Windows (approx 10 seconds) Plug in monitor Right Click Desktop Click ‘Display Settings’ Drag Scaling slider to 125% Click Apply Everything looks great. OSX High Sierra/Mojave (approx 2.5 hours) Plug in monitor The screen doesn’t look right, text and black on white elements are blurry and have chroma ‘bloom’ around them. Open System Preferences Click Displays Look relevant settings There are none. Google it, not sure the exact issue, so try ‘OSX external display fuzzy text’ Read 4 top links that are a collection of forum posts where die-hard Mac users tell me that: This is just the way it is with Mac OSX is ‘better’ because it displays fonts differently and this can make them blurry. Deal with it. My eyes are at fault because I’m comparing it to a Retina screen now and the Retina is SO good that everything else looks blurry. I need to buy an Apply display Try enabling or disabling font smoothing. Decide to try the font smoothing thing. Open System Preferences Click General (weirdly this is not considered a ‘Display’ setting) Font smoothing is enabled, so I try disabling it. It doesn’t fix the problem. Re-enable font smoothing. Back to Google. Finally find a forum post that explains the problem is that OSX incorrectly forces the color mode on some external screens to YPbPr/YCbCr instead of RGB. Open System Preferences Click displays Look for Color Mode setting It does not exist in OSX Eventually find this excellent blog post with a fix: https://spin.atomicobject.com/2018/08/24/macbook-pro-external-monitor-display-problem/ Jaw drops at complexity of the fix - recovery mode?!!?! Decide to go for it. Download the script from GitHub Run the script - it writes a new EDID file. Shut down Mac Boot into Recovery Mode Open Disk Tool Mount the FileVault Encrypted disk Enter password Close Disk Tool Open Terminal Copy the EDID file created to the correct System folder Reboot IT WORKS!!! No more text blurring and color bloom. Celebratory beer. Things are still too small on the external display however, time to tackle the Scaling. Open System Preferences Click Displays Click the ’Scaled’ radio button. Weird, all it does it give a list of alternative resolutions. Try some alternative resolutions, they all look blurry and awful, as expected. Look for other settings related to Scaling. There are none. Back to Google Read through the top links which are all blog posts where die-hard Mac users tell me: This is just how it is with Mac. I need to buy an Apple approved display. That lowering the resolution is the same as scaling (FML you idiots) Eventually find some posts that talk about specific ‘HiDPI’ scaling options by pressing the ‘Option’ key while clicking the Scaled radio button. GO back to Display preferences, hold down Option and click Scaled. Still there are no HiDPI options. Google how to enable HiDPI Find this article: https://www.tekrevue.com/tip/hidpi-mode-os-x/ Open Terminal Run the command Go back to Display Preferences Still no HiDPI options Back to Google. Eventually discover that OSX only natively supports HiDPI modes on monitors with specific Aspect Ratios. (This is completely undocumented by Apple - Thanks Apple!) Google how to set custom resolutions. Find post talking about some software called SwitchResX. Download SwitchResX Baulk at the bizarre user interface. Find the ‘supported’ resolution options for my Screen - there are lots more than in the Apple settings dialog, including some HiDPI ones. Try some HiDPI options, they look good but they are the wrong Aspect Ratio, so there black bars at the sides of the screen. Back to Google “custom HiDPI resolutions in OSX” Links back to SwitchResX FAQ https://www.madrau.com/support/supp...n_I_define_a_new_HiDPI_re.html?TB_iframe=true Open the ‘Manual Resolutions’ tab in SwitchResX Discover this part of the app only works if you disable System Integrity Protection. Can’t quite believe that you need to disable SIP to set a custom resolution, so Google it, end up back at the SwitchResX website where the author has a similar opinion. https://www.madrau.com/support/support/srx_1011.html Sigh. Shutdown Restart in Recovery Mode Open Terminal Enter command to disable SIP Reboot. Open SwitchResX Go to Manual Resolutions tab. Promted for ‘Scaled resolution’ parameters. No documentation on this. Take a guess that as I want 125% scaling I need to multiply my monitors Native resolution by 1.25 in both dimensions. Save the Custom resolution. Try to apply it and eventually realize that you have to Reboot again before this can be applied. Reboot Apply custom resolution. Partial success! Scaling has worked, aspect ratio is correct but everything is way to ‘big’ on the screen. Looks more like 175% scaling. Scratch head and have a think. Realize I did my math wrong. If I want 125% scaling I want to create a virtual resolution of 175% of my screen’s native resolution which will HiDPI scaled down to an effective resolution of 85% of my native resolution making everything appear… ??? 15% Larger?? Brain hurts. Close enough I decide. Try it with virtual resolution of 4480 x 2520. Reboot to save the new resolution. Open SwitchResX Set the screen resolution to the new manual HiDPI setting. OH MY GOD IT WORKS!!! I have a smooth scaled external monitor image which looks almost as good as the Retina!!!!! Realize I now have to pay for SwitchResX after 10 days Refuse to pay $14 Scratch head, surely SwitchResX isn’t doing anything that advanced, probably just editing the Overrides files like the RGB fix Take a look at the overrides file, sure enough, SwitchResX just adds the custom resolutions in here Back to Google. Find great free tool and guide for encoding the custom resolution data: https://comsysto.github.io/Display-...or-with-HiDPI-Support-For-Scaled-Resolutions/ Realize the custom scaled resolutions are still not available in System Preferences, hidden somehow. Another undocumented OSX ‘feature’. Back to Google. Find the awesome free tool RDM to enable the hidden resolutions. https://github.com/avibrazil/RDM Install RDM Finally!!! It all works, for FREEEEE! Shutdown Boot into recovery mode Re-enable SIP Reboot. Done! Gotta love OSX.