The seller is a member here in the forum: Doorsch.
I am sure if you send a pm to him, he will answer all of your questions. Also I think he wouldn't sell the stone as thuringian if he was not sure as much as possible that the hone is one!
As for the difference in color of thuringians in general some short remarks:
The color indicates the layer from which the stones are mined. From these layers the yellow-green layer is superior to the other layers, which are green/gray/blue. This is because the abrasive particles are smaller and from another shape in the yellow green layer than in the other layers. There have been some investigations on this matter in Germany the last 80 years, beginning with studies of Max Volk in the 1930 til 1960 years.
Whereas the particles in the yellow-green layer have a size of 1-10µm, the particles reach an upper size of 20µm in general, the quarzite up to 50 microns in the blue layers. Also the chlorite, which is a main part in the yellow-green layer, less in the other colors, forms round agglomerates that captures the abrasive quartz particles. Thats why the yellow green stones are finer than the other colored thuringians. On the other hand, the material binding in the Y/G thuringians is less compared to the other layers, so raising a slurry is easier and will set more abrasive material free. That causes that the Y/G stones might be faster in honing with slurry even though they are finer.
All this said you still have to keep in mind: The differences are there, but they are small! Thuringian stones in general are superior. Also there are differences in the quality of each layer, so that sometimes the Y/G layer may have less quality to a grey/green one.
Whatever color you got - the honing capabilty makes the stone not the color! Enjoy your catch and report how it will work for you!