multi colored screen when shutting down iMac

I am having the same problem. I bought the 27" iMac 2 weeks ago. At first it was very random and infrequent. It started out as a small block of pixelation. The 3rd time, it filled my screen with the horizontal lines. Now, it is happening almost every time I shut down. And it's not always the same pattern and colors. Has anyone found a resolution?

Thanks (and not sure why the photo is inserted upside down!)

I have had some luck selecting alternate scaled displays. My iMac does not show the horrible pixels upon shutdown. The problem is, I do not like any of the alternate scaled displays. They are either too large or too small.

When I select DEFAULT under scaled display, it reverts back to the unscaled default display. And then the shutdown pixel problem happens again.

Apple needs to fix this!!! A Sierra software update is needed!

Selecting Default in the Scaled settings then reverts to "Default for Display" (not scaled). Then the problem returns.

There is another thread on this problem iMac 27" 5K Late 2015 screen artefacts on shutdown Restoring my 2015 5k to El Capitan for me cured the issue but I want the sierra issue to get resolved. Its some kind of software/driver issue, Sierra seems definitely glitchy on these iMacs.

My 27" retina display has the very same issue. I just bought this 3 days ago. I have tried various methods to shut down and none of them are successful. I almost thought I had it when I immediately hit the return button after clicking on shut down. It worked twice and then failure! I hope somebody figures this out. Brand new and issues is not a good thing.

I would do a hardware test on yours just to be sure and contact Applecare as well, mines only done it since 10.12.2 its a year old almost. Also its very intermittent, and I have reinstalled clean 10.12.2 and I am now testing to see if it happens again.

I may have stumbled across a solution to this issue. I have tried it several times and it seems to work. When I am ready to shut down the machine I first put it to sleep. I wait about 10-15 seconds, wake it up and shut it down reasonably quickly. I don't get the multi-colored screen. When I just quit what I'm doing and go to shut down I get the crazy screen again. Hmm.... Maybe?

It has to do with Final Cut, iMovie and photoshop. Before I bought the mac, I had a MacBook pro and it was chocking with running Final Cut that it was overheating so i notice that whenever I hear the fan going quite hard (normal during video editing), and I shut it down, that's when it happens. Most likely we are close to or past a burnt out graphics card which should not be the case seeing it is 2g ddr5. It really is an overheating issue more than anything I'm sure, but it will soon lead to a damaged graphics card, or worse, faulty motherboard

I have this Problem too on my iMac (Retina 5K, 27-inch, Late 2015) running 10.12.2 my screen normally has more pink and blue colours.

I've done all the resets as told to by apple support.

I even have a default apple background (not that I think that will help)

Even been to apple store, but they could recreate the problem as intermittent. So sent home with out solving the problem.

Any help would be great apple, as had this problem for about 3 months now.

iMac Retina, mid 2015.

Same screen problem since upgrading to OS Sierra. Doesn't happen every time - yesterday, for example, it happened once out of four shurdowns, but some days it has been more often. (I have similar screenshots to those shown here.)

I have the same imac just got it 2days ago . I also get a green screen when shutting down ,I notice that instead of clicking shut down and just let the timer run down ,it shuts down the right way. Being that it's less than a week old I might return it. I was trying to get away from windows so far not to happy with apple😠

Has anyone found a solution for this problem or taken their iMac in for repair? I've had this problem since I first purchased my iMac in January 2017. It happens far less frequently now, but it still worries me. I'm planning on taking it in for repair because I wonder if it's a bad graphics card.

I switched to the next display resolution setting from the default setting can fix this problem

What is NVRAM?

A small amount of your computer’s memory, called “non-volatile random-access memory” or NVRAM, stores certain settings in a location that OS X can access quickly. The settings that are stored in NVRAM depend on the type of Mac you're using, and the types of devices connected to it.

Information stored in NVRAM can include:

• Speaker volume
• Screen resolution
• Startup disk selection
• Recent kernel panic information, if any

If you experience issues related to these features, you might need to reset the NVRAM on your computer. For example, if your Mac starts up from a startup disk other than the one you've specified in Startup Disk preferences, or if a question mark icon appears briefly when your Mac starts up.

What is safe mode?

Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks, and prevents some software from automatically loading or opening. Starting your Mac in safe mode does the following:

• Verifies your startup disk, and attempts to repair directory issues if needed
• Loads only required kernel extensions
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, Kernel cache and other system cache files

Together, these changes can help resolve or isolate issues related to your startup disk.