How to fix macOS external display colour, resolution, or scaling issues on connected monitors

Summary

This guide helps you troubleshoot and resolve: How to fix macOS external display colour, resolution, or scaling issues on connected monitors. Follow the steps below to fix the issue.

Common Causes

If your external monitor connected to your Mac is showing the wrong colours, blurry text, or odd scaling, the issue is almost always fixable through macOS Display Settings. This guide walks you through adjusting resolution, refresh rate, colour profiles, and other settings to get your external display working correctly.

Quick Fix Steps

Before diving into detailed settings, try these common fixes first:

1. Disconnect the cable from both ends, then reconnect firmly.
2. Try a different port on your Mac if available (USB-C, Thunderbolt, HDMI).
3. Test with a different cable — faulty cables are a frequent cause of display issues.
4. Restart your Mac with the monitor already connected and powered on.
5. Reset NVRAM/PRAM by shutting down, then holding Option + Command + P + R for 20 seconds after powering on.

Detailed Instructions

Adjusting Resolution and Scaling

1. Click the Apple menu and select System Settings (or System Preferences on older macOS versions).
2. Click Displays in the sidebar.
3. Your external monitor will appear as a tile — click on it to select it.
4. Look for the Resolution or Display Resolution dropdown.
5. Choose one of the following:
   • Default for display — recommended starting point
   • Scaled — reveals additional resolution options including the monitor's native resolution
6. For the sharpest image, select the resolution marked as (native) or the option that matches your monitor's panel resolution (e.g., 2560 × 1440 for a QHD display).

Fixing Colour Issues

1. Open System Settings → Displays.
2. Select your external monitor.
3. Click the Colour Profile or Profile dropdown.
4. Try a different profile from the list — start with sRGB IEC61966-2.1 or Display P3 for accurate colours.
5. If colours look washed out or oversaturated, switch profiles and observe the change.

For more advanced colour calibration:

1. Open System Settings → Displays → Colour Profile.
2. Click Calibrate (or open Spotlight with Cmd + Space and search for Display Calibrator Assistant).
3. Follow the on-screen prompts to create a custom colour profile.

Adjusting Refresh Rate

1. Open System Settings → Displays.
2. Select your external monitor.
3. Click the Refresh Rate dropdown (visible only on supported displays).
4. Choose the highest rate your monitor supports, typically 60Hz, 120Hz, or higher.
5. If you experience flickering or instability, drop to the next available lower rate.

Enabling HiDPI Mode (Sharper Text)

HiDPI mode renders text and interface elements at double resolution, making everything appear sharper on external displays.

1. Open System Settings → Displays.
2. Select your external monitor.
3. Under Resolution, look for options labelled with icons rather than pixel dimensions — these are HiDPI modes.
4. Select the HiDPI option that gives you usable screen real estate (often labelled simply as a smaller text/larger text toggle).

Troubleshooting

External Display Not Detected

• Check the cable connection at both ends.
• Try a different cable or port.
• Reset the SMC on Intel Macs: shut down, then hold Shift + Control + Option + power button for 10 seconds.
• Apple Silicon Macs don't have an SMC reset — simply restart instead.
• Test the monitor with another computer to confirm it works.

Flickering or Signal Dropouts

• Lower the refresh rate.
• Reduce resolution to the next available step.
• Disable HDR temporarily via System Settings → Displays.
• Replace the cable — long HDMI or DisplayPort cables over 2 metres can degrade signal quality.
• Check for macOS updates via System Settings → Software Update.

Wrong Colours or Tinted Display

• Switch the colour profile as described above.
• Disable True Tone in System Settings → Displays if enabled.
• Disable Night Shift temporarily via System Settings → Displays → Night Shift.
• Check the monitor's own OSD (on-screen display) menu for colour temperature settings and reset to default.

Display Scaling Looks Off After macOS Update

1. Open System Settings → Displays.
2. Hold Option and click Scaled to reveal all hidden resolution options.
3. Select your monitor's native resolution.
4. Restart your Mac to confirm the setting persists.

Monitor Works but Shows "Unknown Display"

This typically indicates the Mac isn't reading the monitor's EDID information correctly. Try the following:

• Use a higher-quality cable that supports EDID pass-through.
• Avoid passive adapters where possible — use active adapters for DisplayPort to HDMI conversions.
• Connect the monitor before logging in (at the login screen) so macOS detects it during initial setup.

Still Having Issues?