Fixed a bug where the active color wasn't being set on imported meshes, resulting in no colors displaying in the viewport. This bug has been in the code for a long time. However, the colors have been displaying correctly until recently, so this issue wasn't previously apparent. Also, changed custom color data name from "displayColors" to "displayColor", to match the actual USD primvar name. (This was a typo in the original code.) Note that pull request blender/blender#104542 addresses other issues in the color import code (e.g., converting all color primvars and not just "displayColor", avoiding hard-coding of attribute names, handling all iterpolation types, etc.). However, the current commit is meant as a short term fix to a regression, where the "displayColor" attribute does not render in the viewport at all, until the above pull can be merged.