When you have an image in a specifc color space, lets assume Rec709; I know Photographers are use to color spaces such as ProPhotoRGB etc but for me I'm working with a different arena of color spaces. Anyhow, the display which I'm displaying those images, can only display 94% of Rec709, that leaves about 6% color difference.
I obviously don't want to change the original image, incase it gets viewed on a display which can display the full gamut of Rec709; rather, I want to find and adjust those colors for my specific display so that they match that of the original Rec709 exactly or very close.
From what I understand, soft proofing is what I would need; or is there something else ?
You need to read up on Color Management. You should Edit your images in Photoshop in a Standard Color Space: ProPhoto RGB, Adobe RGB, sRGB, etc. Photoshop is Color manage and your Display's system Profile will be used when Photoshop Renders your images colors on your display. And when you Print you set the ink and paper color profile for your printer Color Profiles in Photoshop's Print Dialog and have Photoshop manage printer colors and you turn off your Printers's Device drivers color management for your Printer's colors. What is Color profile Rec709 for?
If you display can not display a color color management will use the color as close as prosible the display can display.
In any case there will be a difference because the display as my example; is only displaying 94% of the Rec709 gamut. If it were 99%, I wouldn't be posted this question.
It is that 6% difference I want to see what is changing between the actual gamut in the image, and that which my display can display. It may only be small; maybe less green is shown, or; less red is shown for my display. To which I can use an adjustment level or curves and try to match it the best I can.
Basically, I just want to know how to view the color difference using what it is sorta intended to do using soft proofing which doesn't have to be strictly used for print.
There's no way. The display can't reproduce those colors, so you can't see them. Soft proofing is pointless.
Perhaps the "desaturate monitor colors by"-option in color settings could work, just to get a sense of how big, and where, the actual difference is. Most likely it's the red primary, which, somehow counter-intuitively, will mostly affect dark cyans and blues where the red channel approaches 0.
If you soft proof against an ICC profile. For example, you would simulate a color gamut against a calibrated ICC profile, therefore seeing the color differences.
It's not that simple. Soft proof only works when the display has a gamut that covers the source color space. You need to see what you're leaving out. In this case you don't, the colors in question are outside the monitor's capabilities. You won't see any difference.
Now, if you temporarily hooked up a wider gamut monitor, one that fully covers Rec.709, and then soft proofed your Rec.709 file to your current monitor profile - then you would see the difference.
@JJMack "What is Color profile Rec709 for?"
Rec709 is a colour space widely used in video. The primaries are the same as sRGB but the Rec709 transfer function is closer to 2.4 rather than sRGB's close to 2.2 (both have a linear section at the start).