There are a few simple tweaks you can make to resolve the inverted colors. First, try rebooting your Wii U. If that does not work, check your system for any updates you need to perform or if the HDMI port is damaged. This troubleshooting guide outlines all the possible solutions for this problem: Nintendo Wii U Troubleshooting

Make sure that there are no other Wii U devices in use in your household, and that other devices (cell phone, tablet, etc.) are not in close range to your Wii U. These devices can cause interferences in syncing. Our troubleshooting guide explains in further detail how to test for this common issue: Nintendo Wii U Troubleshooting

If your hard drive is one uses the Wii U console as the main power source, it is very likely that it could be the cause for the random freezing. When it takes too much power away from the USB and the console, it can overwhelm the system. Check out this troubleshooting guide on how to test if your external hard drive is the issue: Nintendo Wii U Troubleshooting