Hi kartski1,
It sounds like your external display isn't looking right when connected to your Mac. We're glad you've joined us in Apple Support Communities. Let's see if this helps.
Follow the steps in Get help with video issues on external displays connected to your Mac. This will guide you through troubleshooting your Mac display settings.
Also, if it's 4K display or Ultra HD TV you'll want to check compatibility with your Mac. You'll want to make sure your computer meets the requirements for using these external displays. Use the section, "Check display support" in Use external monitors with your Mac.
If the issue remains after following those steps, let us know what it said when you checked the specifications on your Mac from the advice above.
We hope that helps with your question and take care!