YELLOW "means that it is implemented but has some known bugs." It explains it self. The feature with this has bugs which means unstable for production.
RED "means that someone needs to write the code. The required knowledge to write the code may or may not be known. Please ask on #radeon if you want to get your feet wet on this." This means nobody has been scheduled to handle that type of feature and nobody knows if it can actually be supported for each Radeon model.
Radeon graphics does support video hardware decode since the first Radeon model in Windows, but ATI at the time wrote it so horrible that it was unstable in Windows. AMD not providing any documentation for UVD just prove that I am right that not even AMD is willing to be completely open source to the community. This may change, but I still doubt it.
You need to read the legend before coming here to correct me.
There are many features that the open source Radeon driver does not support yet. It seems you do not see those features listed as TODO and this means it needs those features to be compatible with OpenGL spec or provide the features the Windows drivers includes. As it stands right now the open source Radeon driver is not ready for production systems. It is OK to use for simple 2D tasks, but for OpenGL will have a problem. Gamers or users running 3D applications should still use nVidia graphic cards to ease playing their games or using 3D applications in Linux since nVidia's close source drivers are ready for production if you like them or not.