There is no such thing as "plain old RGB". You CAN have, as you've seen UNTAGGED RGB files, but all that means is there is no reference as to how to interpret those RGB numbers. When you open that untagged file in Ps and leave it not color managed, Ps has to assume something, so it assumes the file to be in whatever RGB color space you have set in your color preferences. It's pretty much like using the Assign Profile command but without actually doing it and only having the choice of whatever you had in your color settings. The best you can do in this case, especially where you have erroneous advice from your industry forum, is to make sure that your monitor is calibrated properly, open that original untagged RGB file and use the Assign Profile dialog command to assign different color space profiles to the file until you've found the one that looks the best on your screen. Given that those untagged files were probably created in an application that was not color managed, they were, in effect in what's known as "Monitor RGB", and most monitors are either close to sRGB or Adobe RGB, your first two guesses are going to be the closest to being right. My vote goes to sRGB.
The other thing you might consider is how these files are going to ultimately displayed and on what devices. If these flight sims are viewed on a regular television then a color space like REC709 might be more appropriate. If they are primarily viewed on computer screens, then sRGB would be your best guess. FYI, REC709, which is the current commercial broadcast standard, is simply sRGB with a 2.4 gamma.
My gut feeling is sRGB, as those who dont alter their systems end up with sRGB.
news to me though that 'leave as is' actually doesnt do so and converts it to my working space, the option I didnt pick.
So if I want it as sRGB I need to apply that profile at that opening phase, or if I am making something from scratch, then I need to go to colour settings and choose sRGB, though with my monitor calibrated to 6500K AdobeRGB1998 I am then worried as to am I designing to screen now, what can I trust in.
If I make flight sim skins as AdobeRGB1998, will the sim struggle if its engine was designed for sRGB.
I dont want to recalibrate screen to sRGB then forget to revert it to AdobeRGB when working on photos for publication !
Not sure what I should do in fact if running profile sRGB on a AdobeRGB monitor, but probably say sod it and carry on with AdobeRGB.
Just a technical aside: RGB 8 bit is where each channel (Red Blue and Green) has 255 values.
8 bit is an 8 place binary number, 1111 1111 which is decimal 255 Binary to Decimal Converter
Anyway I once used Adobe RGB as my workspace and would get untagged images off the net. They would take on a reddish tone when opened in Photoshop.
Photoshop took the raw sRGB values and not knowing where they came from, treated them as Adobe RGB.
Untagged means you created them in an Adobe RGB space, but did not label the bottle. Windows is pretty much sRGB native and most viewers did not read tags anyway. Placing an Adobe RGB image into an sRGB space meant the colors would desaturate or look muddy.
Why is that? A color space defines what those numbers mean, or what color is slapped on the screen
Pale Red Purple is 229 173 193 in Adobe RGB space but 247 175 195 in sRGB. So take the raw Adobe RGB numbers into sRGB without any color management and you will see the difference.
So maybe what your customer is saying is that they will handle the conversions. The thing is does your customer know you are using Adobe RGB? Is your customer working in sRGB and doesn't know this?
Anyway this is just a summary. I leave the thorny details to those with more experience in Color Management matters.
Merlin, we need to be absolutely clear on one thing:
You cannot work without color management (untagged) on a wide gamut monitor. It relies on remapping the document data into your monitor profile. Without that, it will display oversaturated.
As Gene pointed out, the color space defines what the numbers mean, what specific color comes out.
Since this is a non-color managed process, you can safely assume sRGB. But you can't work with untagged files, not with that monitor - so you must assign sRGB and work with that.
Working without color management is something I never recommend, but if you have to do it, it requires a standard gamut monitor. Its native response is close enough to sRGB that most people won't notice or mind the difference, as long as the file is created in sRGB with sRGB numbers.
Optionally you can set your unit to the sRGB preset, which will "dumb it down" to sRGB.