External HDMI monitor shows dulled colors and low contrast only when MacBook lid closed in clamshell mode

Environment

MacBook Pro (Apple Silicon M1 Pro) running macOS 13.5 connected via USB‑C dock to an external 4K HDR-capable HDMI monitor. The MacBook is used in clamshell mode (lid closed) with external keyboard and mouse. Built-in display disabled in clamshell mode.

Symptoms

Video and desktop appear correct when the laptop lid is open; after closing the lid and using only the external monitor, RGB colors become washed-out, contrast reduced, and HDR content displays incorrectly (no deep blacks). Opening the lid instantly restores expected colors on the internal display and external monitor. Problem recurs every time lid is closed to enter clamshell mode.

Observations

Monitor EDID shows HDR10 capability and 10-bit color. System Report -> Graphics/Displays lists external monitor as 4K@60 and reports HDR support when lid open. When lid is closed, System Settings -> Displays shows the external monitor active but HDR toggle appears disabled in some apps. Color profile in Display Settings switches from the monitor's calibrated profile when lid open to a generic profile when lid closed. No kernel panics or GPU errors in logs. Dock firmware up to date; macOS was recently updated to 13.5. SMC/PRAM-style resets do not apply on Apple Silicon.

Already attempted

Tried different HDMI cables and using a direct USB‑C to HDMI adapter bypassing the dock — issue still reproduced when lid closed. Created a custom ColorSync profile using Display Calibrator Assistant while lid open and applied it; opening lid keeps good colors, but after closing lid the profile reverts to a generic profile. Restarting the Mac with lid closed not practical. Booted into safe mode and tested; color change still occurs when entering clamshell.

Question

Which macOS settings or hardware interactions control switching of color profiles and HDR capability when entering clamshell mode? What reversible steps can I take to prevent the system from reverting to a generic color profile when lid closes, and when should this be escalated to Apple support as a possible firmware/macOS bug?

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AI DIAGNOSTICS

Incident analysis

Updated 1w ago• Trouble ID

Most likely causes

ColorSync profile association is linked to the internal display state and reverts when the system re-enumerates displays on lid close. 90%

macOS disables HDR or switches to a fallback color profile automatically when the internal display is inactive (clamshell), due to display topology detection or an internal capability mismatch. 85%

A macOS regression in the current OS that mishandles HDR/color profile selection on Apple Silicon when entering clamshell mode. 70%

Summary

The system is switching display capabilities or color profile when the internal display goes inactive during clamshell mode. macOS may be choosing a fallback color profile or disabling HDR when it detects a different display topology (internal display off). Since the profile change persists despite custom profiles and happens even with direct adapter, it is likely macOS logic around clamshell mode rather than dock firmware or cable. Apple Silicon may also handle external display color differently when internal display is off.

Suggested Fixes

Diagnostic step 1

In System Settings → Displays, while in clamshell mode, manually re-select the monitor's native color profile; if it sticks, create a lightweight automation (or script using displayprofile tools) to reapply on lid-close event. Document exact steps to revert.

Diagnostic step 2

Test with the internal display disabled but lid open (use an external keyboard to blank the internal display) to see if the state rather than the lid position triggers the change. If color remains correct, lid-closing triggers the policy.

Diagnostic step 3

Collect logs: run Console.app and capture system and WindowServer log entries around the moment of lid close to identify Display re-enumeration events; gather EDID reports for both lid-open and lid-closed states.