: I don't know since when this is possible, but as of 1.4.83 (maybe earlier, I can't tell) it has turned out that the in-game design tool will only work on custom objects when the group ID of their catalogue instance and object definition (COBJ and OBJD) is 0x00000000 and the first half of the instance ID too. Otherwise, custom objects will throw a “Script Call Failed” error when trying to recolour them in-world.
This is probably not a good thing, since it makes ID collisions a lot more likely and you also said that all custom stuff should
use a custom group ID and so on .. dunno, would this be a bug? Do you think you can do something about this on your side; or alternatively, do you think there's a chance of getting this to work on “regular” custom objects (with group 0x8000000 or whatever and 64bit IIDs) by way of a script mod, perhaps? I tried to look into the latter before but it went way over my head -- maybe someone like @scumbumbo
could comment on the doability of that.