Im on an oldish version of OS X, mainly because I do a lot of development work with various microcontrollers etc, and Im afraid of breaking toolchains and hardware tools that I use for this work.
But I wonder if anyone else has seen this and knows what is happening? Maybe I just need to update finally.
Known bug. It has to do with the changes to colour space handling made between RC1 and release, probably a null pointer when some object doesn't get created/retrieved.
None of us have a machine with macOS 10.12 installed so it's difficult to debug and any attempts at fixes would have to be blind.
On the issue tracker: https://github.com/OpenTTD/OpenTTD/issues/8066