Chrome Version       : 71.0.3578.94 (Official build) beta (64-bit)
URLs (if applicable) :
OS version               : 11151.59.0 
Network (such as Cable/DSL/Dial up etc):  Wi-Fi
Audio/Video format (if applicable):   VGA cable @ 1080p on ACER External monitor
Special chrome flags (if applicable): none

Video issue, Audio issue, both, neither?  VIDEO

Hardware:  ACER Chromebook 15 CB515-1HT-P39B
TNP USB Type-C to HDMI/ 4k VGA Gigabit Ethernet USB 3.0 Hub Multiport Adapter  with VGA connector.  (you can find this on Amazon).
ACER G246HL 24 Inch 1080p Monitor

What steps will reproduce the problem?
(1)  Connect adapter to chromebook, connect VGA to to adapter and monitor
(2)  Set as extended display

What is the expected result?
Same quality image from Chromebook as the same monitor gets from Windows over a similar connection

What is the actual result?  Washed out, dull color palette.

Any additional information (anything else which may help us debug the
issue)?

Lowering the resolution down to 1680x1050x60Hz immediately caused the full vivid color to show using my background wallpaper. Reverting back up to native 1080p returned back to dull color palette.  Very reminiscent of Pixel 2 XL in 'unsaturated' color mode.  

It can't be the monitor, as I use it in 1080p on a Windows machine all the time and the monitor shows bright vivid color.  Only when it is used as a Chrome OS extended screen in 1080p does the color range get hammered.  I also tried the same test on a separate hp monitor, with similar results.  So, it isn't the monitor.