The error you're encountering, "Color hexadecimal length must be 6, received: ff9a00ff," suggests that there's an issue with how the color values are being interpreted during the import process. This is likely due to the 'Tint Black' functionality, which uses an 8-character hexadecimal to represent colors (including alpha), whereas the error message indicates an expectation of a 6-character hexadecimal (without alpha).
Given that both your runtime and Spine Editor versions are 4.1x, compatibility should not be an issue. However, the error message you're seeing was specifically addressed in a forum post discussing a runtime error related to color hexadecimal length. The post suggests that the error arises from a discrepancy in how color values are parsed by the Spine-Unity runtime.
To resolve this issue without removing the 'Tint Black' functionality, ensure that you are using the latest version of the Spine-Unity runtime. There might have been updates or fixes related to this issue after your current version. If updating does not resolve the issue, it could be a bug that needs to be reported to the Spine development team. Unfortunately, without direct access to bug tracking or the ability to submit a bug report on your behalf, the best course of action is to ensure your runtime is up to date.