macOS Ventura: HDR video shows washed-out color and green frames on external HDMI monitor connected via Thunderbolt 4 dock

Environment

MacBook Pro 14-inch (M1 Pro) running macOS Ventura 13.5, connected to Belkin Thunderbolt 4 dock via native Thunderbolt cable; dock uses HDMI 2.0 to LG 4K60 HDR monitor. Problem started after macOS update to 13.5.

Symptoms

When playing HDR content in Safari and Apple TV app, the external monitor displays washed-out colors and intermittent green frames for 2–5 seconds; system video playback continues on internal display fine. Video color looks correct on internal display and when switching the external monitor to SDR mode. Problem is intermittent but reproducible within minutes of starting HDR playback.

Observations

System Settings > Displays shows external monitor HDR capability as 'Supported'. Activity Monitor shows low CPU usage but 'WindowServer' spikes coincide with green frames. When unplugging the Thunderbolt dock and connecting monitor directly via USB-C to HDMI adapter (bypassing dock), HDR playback is correct. Logs in Console show repeated GPU/IOKit warnings referencing 'display stream' and 'EDID parse failed' while green frames occur. Same dock works fine with a different non-HDR monitor. Reverting macOS to previous Time Machine snapshot unavailable.

Already attempted

Reset SMC/SMC-like functions (shutdown and power cycle), NVRAM reset equivalent on Apple Silicon by safe shutdown, toggled 'High Dynamic Range' and 'Optimize video streaming' options in System Settings, updated monitor firmware to latest version, updated dock firmware from vendor tool. Tried different HDMI cables, and different HDMI inputs on the monitor. Issue persists only when dock is in the chain and HDR content is enabled.

Question

How can I reliably diagnose whether the fault is due to macOS HDR handling via Thunderbolt alt‑mode, an EDID/HDCP negotiation bug in the dock, or a driver/firmware regression in Ventura, and what reversible steps should I take to restore correct HDR output for now?

Post timeline

COMMUNITY RESPONSES

Verified community troubleshooting

0 replies

No answers yet..

Showing 0 of 0 community responses

AI DIAGNOSTICS

Incident analysis

Updated 1w ago• Trouble ID

Most likely causes

EDID or HDCP negotiation failures resulting in temporary fallback to an unsupported color pipeline, causing green frames while WindowServer reconfigures framebuffer. 95%

Thunderbolt dock firmware/bridge chip incorrectly handling HDR metadata (color space primaries, EOTF) or misreporting EDID causing macOS to choose unsupported pixel format. 90%

Monitor reports HDR support but expects different color depth/format (e.g., requires YCbCr 4:2:2) and the dock forces incompatible format. 60%

Summary

Behavior suggests negotiation/handshake issue for HDR color metadata or pixel format over the Thunderbolt→HDMI conversion path. The fact that direct connection works and dock connection fails implicates the dock's DisplayPort/HDMI converter or how macOS uses the Thunderbolt alt‑mode via the dock. Console EDID/stream warnings and WindowServer spikes support a driver-level interaction with display capabilities. This is likely a regression triggered by macOS update or a dock firmware/EDID handling mismatch under HDR modes.

Suggested Fixes

Diagnostic step 1

Capture display negotiation logs: in Console.app filter for IOKit, WindowServer, and 'display' messages during reproduction and save logs for vendor escalation. This is read-only.

Diagnostic step 2

Test with direct USB‑C to HDMI/DisplayPort adapter to confirm dock is the differentiator (already tested — direct works). As a workaround, use the direct adapter for HDR playback until root cause is fixed.

Diagnostic step 3

Set Display settings to force SDR on the external monitor to avoid green frames while streaming HDR; reversible from System Settings.