Blender 5.0 put a working colour space inside the blend file itself. The default is Linear Rec.709. You can also choose Linear Rec.2020 or ACEScg.
So my file and your file can now disagree. Append my material into yours and Blender converts the colours for you. The release notes say that conversion is only an approximation, and that manual fix-ups are often needed.
I ship .blend files to people on every version from 4.2 up. So I measured what that sentence costs.
What I put in the test file
I built one file in Linear Rec.709 with nine flat base colours. Red, green, blue, cyan, a skin tone, 18 per cent grey, white, orange, and one messy material.
The messy one holds a Value node, a colour ramp, an emission shader, a packed sRGB texture and a packed Non-Color map. The file also has a point light and a world colour.
Then I appended all of it into an ACEScg file. Blender 5.1.1, repeated in 5.0.1 with identical results.
Appending moved every number and no colour
Every base colour was rewritten on the way in. Pure red went from 1.0, 0.0, 0.0 to 0.613, 0.070, 0.021. My skin tone went from 0.5, 0.27, 0.19 to 0.407, 0.285, 0.205.
Grey did not move. Both 18 per cent grey and pure white came through untouched.
Then I wrote both sets of swatches out as 8-bit sRGB. Through Standard and through AgX, all nine patches matched. Zero difference out of 255, on every channel.
So the numbers change and the picture does not. Linking a library gave exactly the same result as appending.
What it leaves alone
Image pixels are never touched. My packed sRGB PNG and my packed Non-Color map both came through unchanged, with their colour space tags intact.
Roughness stayed 0.35. The Value node stayed 0.5. Emission strength stayed 12, and the light kept its 1000 watts.
The light colour did change, from 1.0, 0.55, 0.2 to 0.809, 0.577, 0.255. So did the world colour. So did the coloured stops on my colour ramp.
That last one is worth knowing. A colour ramp driving a mask is not really a colour, but Blender treats it as one.
Grey stops survived. Coloured stops did not.
The other direction is where it breaks
Then I ran it backwards. Same test built in ACEScg, appended into a Rec.709 file.
ACEScg holds colours that Rec.709 cannot reach. Blender clamps them into range.
A saturated ACEScg green of 0.2, 0.7, 0.05 arrived as 0.0, 0.772, 0.0. Red and blue were flattened to zero. An emissive of 4.0, 0.2, 0.1 arrived as 1.0, 0.0, 0.0.
Through AgX the worst patch moved 126 out of 255 on one channel. Saturated cyan moved 107. A soft brown that was already in range moved nothing.
The same test through Standard showed a maximum of 1. Standard clips those colours anyway, so it hides the loss. Test in the view transform you actually render with.
Old Blender just reads the raw floats
Blender 4.5 has no working space. It reads whatever numbers are in the file as Rec.709.
I saved my ACEScg file and opened it in 4.5.3 LTS. Green moved 47 out of 255, blue 43, cyan 38, red 28, the skin tone 11.
The only warning I got was that the file came from a newer binary and data may be lost. Nothing mentioned colour at all.
The same nine materials saved as Linear Rec.709 opened in 4.5.3 with zero difference. Blender 4.2 LTS dropped off the maintained list in July 2026, and plenty of buyers are still sitting on it.
The HDRI bugs, and when they were live
Two colour management bugs followed the 5.0 release. Both are closed now, and I re-tested one of them.
Bug 150374 gave an imported HDRI the scene working space instead of its own. I loaded an .hdr in 5.0.1 and in 5.1.1, with the working space set to Rec.709, Rec.2020 and ACEScg in turn.
Every time it came in as Linear Rec.709, which is correct. That bug was reported on 21 November 2025 and closed three days later, so only 5.0.0 shipped with it.
Bug 151996, wrong saturation on the built-in HDRIs after a working space change, was closed on 11 February 2026.
What I ship, and what you should do
Linear Rec.709, on everything I send out. It is the default, it converts up into ACEScg with no visible loss, and it opens correctly in 4.x.
Shipping ACEScg would hand the clamp to the buyer. So every .blend I save goes out in Rec.709, including the base mesh packs and the libraries behind my add-ons.
If you work in ACEScg, do the conversion inside your own file. Append my Rec.709 material and let Blender lift it.
I have not tested this through a remote asset library, but that is the same append path. Expect the same behaviour there.
Two habits are worth building. Check the working space before you save a file someone else will open.
And test your worst colour, not your average one. The brown moved nothing. The cyan moved 107.