I just installed the latest release of Media Composer (2018.5) on a fresh install of Windows 10 pro on a new system. I created a fresh user profile.
I was shocked to see that once I AMA linked some footage, the color of the video in the source/record windows was incorrect, looked almost inverted.
I checked the Source Settings of the clip and oddly enough the preview window there shows the correct colors for the clip.
The source and record windows are are set for Rec.709 full range, but any setting I choose from the display color space window doesn't have an impact on the colors.
The project is set for the default YCbCr 709 color space.
I can't find any other setting I would think would change this.
I also have Adobe Premiere Pro, After Effects and Davinci Resolve installed and they all show the correct colors for these clips.
Graphics card is a Nvidia Geforce GTX-1070 TI, connected to a Dell UP2718Q 4k display. Windows 10 Pro 64-bit.
Intel Core I9 7940x (14 cores), 64GB of DDR4 memory installed.