That's clearly explained, then. :)
I don't suppose Safari has a public bug tracker? This sounds like such an awesome "WTF" it'd be fun to read the developers' take. :)
The R and B colour switch in conjunction with the fact that this problem only occurs at non-right angles would indicate that there's a bug in the rendering pipeline that is triggered under specific conditions. Specifically if the transform is at a right angle, then an optimal transform algorithm will be used that processes colours in RGBA format. For all other angles a slower (but prettier) transform pipeline will be used that results in the colour being incorrectly processed in BGRA format. An easy way to test this theory is to set the problem colour to bright green, in which case the bug shouldn't be apparent.
SVG rendering pipelines are really complicated. The quest for optimisation leads to rendering code that has many paths for all the different scenarios. The consequence is that odd bugs for certain conditions are more likely to creep into the code base if you're not careful.
Sorry, I would check myself, but am on Linux and don't have access to Safari 10.