screen corrupted to primary colors after sleep

After approximately hour or more of use when display sleeps and I try to awaken, the Image is corrupted and displays vivid primary colors including desktop. I can correct it if I restart the MAC. Is this a problem with mac system or Monitor? Is there a way to fix it? Have mac mini late 2014 Intel core I-5, 8GB memory, Intel iris 1536MB, Yosemite 10.10.5 will Dell Monitor. 1.12 Fusion Drive.

Welcome to our forums.

You can test if the problem is with the GPU in the Mini or the monitor by substituting another monitor in place of the Dell. Do that first and then we can decide what to do if the problem persists with the test monitor.

You didn't say what connection type? From the Mac mini and into the monitor?

screen image problems

ferrarr said:

You didn't say what connection type? From the Mac mini and into the monitor?

Click to expand...

its a HMDI connection.

I do have backs Hard disk and iCloud - thanks for the reminder though

Will look for another monitor to verify source of the problem. Thanks