Very good question. I am using an LG - 27" 4K UHD Monitor and an LG - 34WL500-B 34". I've been editing it on both monitors and the colors still look awful regardless of which monitor I edit the video on.

Elgato provided this article here on how the video attributes for videos in HDR. I watched the video -- It may be that I need to mess with the color space within the video itself, as mentioned in the video. If so, not sure which one would fit best...

Are you opening Log or HLG HDR?

https://www.vegascreativesoftware.info/us/forum/faq-how-to-post-mediainfo-and-vegas-pro-file-properties--104561/

What profile is set for your project in the media settings?

Specs on the 34W aren't saying much, but it says HDR10 so I'm going to assume that's accurate.

Check the project settings.

EDIT: Others beat me to it. Should have refreshed the page.

Here is the log for that video:

Video
ID                                       : 1
Format                                   : HEVC
Format/Info                              : High Efficiency Video Coding
Format profile                           : Main 10@L5.1@High
Codec ID                                 : hev1
Codec ID/Info                            : High Efficiency Video Coding
Duration                                 : 2 h 15 min
Source duration                          : 2 h 15 min
Width                                    : 3 840 pixels
Height                                   : 2 160 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 59.940 (59940/1000) FPS
Original frame rate                      : 59.940 (60000/1001) FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 10 bits
Source stream size                       : 42.5 GiB (75%)
Language                                 : English
Encoded date                             : UTC 2020-06-10 04:57:43
Tagged date                              : UTC 2020-06-10 04:57:43
Color range                              : Full
Color primaries                          : BT.2020
Transfer characteristics                 : PQ
Matrix coefficients                      : BT.2020 non-constant
mdhd_Duration                            : 8140063
Codec configuration box                  : hvcC

Audio
ID                                       : 2
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 2 h 15 min
Source duration                          : 2 h 15 min
Bit rate mode                            : Constant
Nominal bit rate                         : 320 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 SPF)
Compression mode                         : Lossy
Source stream size                       : 308 MiB (1%)
Language                                 : English
Encoded date                             : UTC 2020-06-10 04:57:43
Tagged date                              : UTC 2020-06-10 04:57:43
mdhd_Duration                            : 8139715

P.S., I switched the HDR Setting from HD10 to HLG, but the brightness of the video is still a bit off. View attachment below:

Also, below are the media settings

Very good question. I am using an LG - 27" 4K UHD Monitor and an LG - 34WL500-B 34". I've been editing it on both monitors and the colors still look awful regardless of which monitor I edit the video on.

I looked after the price of both Monitors:

LG - 34WL500-B 34" IPS LED UltraWide FHD FreeSync Monitor with HDR - Black=$349.99
LG - 27" 4K UHD Monitor - Black/White (LG UltraFine Display)=$449.99

I'm quite sure they are just normal 8-bit Computer monitors and have nothing to do with true HDR.

So you should do:

1, in project choose the sRGB(ACES) as your ViewTransform; a view transform is a Reference Preview, means I do my editing in a colorspace (as reference) and output my editing in another colorspace (as reference rendering).

2, your source media is an HDR-clip, you also must tell the ACESystem its properties (between Rec2020 ST2084 1000 to 4000 nits), otherwise the ACES cannot know what is on the timeline.

3, if you don't use/understand the fundamental videoscope tools you will go no deeper about what NLE-pro is.

Right click on your HDR media. Go into properties at the bottom. In there, you will see a drop down menu that lets you specify the color space of your media (you may have to click through a tab or two to find it). We need to know what color space your media was recorded in to be able to tell you specifically which color space will work for your file, but you can try Rec2020 ST2084 (1000 nits). See if that helps. The way you can tell if your color space is set up properly is by looking at the RGB parade video scope. If it does not exceed 100 nits, it isn't working right, it should spread all the way to somewhere around 1000 nits.

Also, Windows itself must be in HDR mode for HDR to work. To enable this, right click on your desktop, go to display properties, and in there you should see options to enable windows HDR mode (sometimes it's listed as deep color mode). Make sure you launch Vegas AFTER doing this. To be sure it is working, go to preferences in Vegas, display adapter settings (saying that from memory, it may be called something slightly different), and select the HDR monitor you have connected. You should see an "enable HDR output" checkbox at the bottom, make sure that is checked.

If you do not see a windows HDR mode setting, you either have the wrong monitor selected, or your monitor does not support HDR, or it is hooked up to a connection that doesn't support HDR (like a display port to HDMI adapter that doesn't support HDMI 2.0).

Here's a video tutorial illustrating what I said above. Note, I used media here recorded with my Panasonic S1 in the VLOG/V-Gamut color space, so that is what I had to select in the media properties in order to make it work right. Your media may require a different setting, which is why I recommended you start at Rec2020 ST2084 (1000 nits) color space.