Absolute color tables map the colors of crafting material to a standardized color space.
Home crafting software often relies on RGB values, since RGB colors can be used to simulate the crafty result on-screen.
Professional crafting software often maps material colors to an official Pantone-palette internally, but since the Pantone Corporation has a very specific interpretation of proprietary rights combined with a very restrictive licensing policy, sharing such tables freely or using them in open source software might pose a legal risk.
This policy may also be the reason why some thread manufacturers only provide an interface to find the thread that matches an individual Pantone color, rather than publishing the complete table online.
The Open Craft Database is a project aimed at collecting Lab values for yarns and beads of all manufacturers.