What do the colors in backward-cpp mean?

I am using the stack printing library Backward: https://github.com/bombela/backward-cpp

Which automatically prints a stack trace of the current program when called.

It also colorizes it which is nice. Now, my issue is that I am trying to understand what on earth does each color mean.

The documentation doesn't seem to specify and I was unsuccessful at finding this information by looking at the source code.

For example:

In that image, yellow seems to indicate the functions that have been put on the stack, but then one of them is purple. I know the purple one triggers a validation error in vulkan, but I am not sure if Backward would have a mechanism to understand that.

According to this purple seems to be used to mark inlined invocations while yellow for non-inlined.