You may see a purple screen if Roku detects the TV or audio/video receiver (AVR) in use does not support required content protection technology, called HDCP.  However, the purple screen could also result from other problems like a faulty HDMI cable or HDMI connector.  

If the issue is a faulty HDMI issue, try these troubleshooting steps to resolve it:
  1. Carefully review the instructions for setting up your Roku player for 4K. Go to the next step if you continue to see a purple screen.
  2. On both your Roku player and your TV or AVR, unplug each end of the HDMI cable.
  3. Power off your TV and unplug its power cord.
  4. Remove the power cord from your Roku player.
  5. Reconnect both ends of the HDMI cable, making sure each connector is attached firmly and securely.
  6. Reconnect the power cord to your TV and your Roku player and wait for both devices to power on (you may also need to press the power button on your TV remote). 
  7. Try viewing the video again.
If the steps above did not resolve your issue, try these suggestions:
  1. Try a different HDMI input on your TV.
  2. Try using a different HDMI cable, preferably, less than 6 feet in length, to ensure the cable you’re currently using does not have any defects.
  3. If you are using an HDMI switch or AVR, try connecting the Roku player directly to the TV.
  4. Try another TV, if possible.
  5. If you are using a computer monitor, try using a TV, if possible.
  6. Try using different Display Settings on your Roku player. You can find these settings under Settings > Display type.
  7. If this is the first time you are seeing this HDCP purple screen after setting up your Roku player, ensure that your TV and/or AVR supports HDCP. You can also contact your equipment manufacturer for more information.