North American Aviation X-15A-2 - External Tanks (part 2)

The riveting process on the X-15 is taking a lot longer then I expected. Meanwhile in the paint booth (Texturing), I've completed the first texture graphic for the 3D Models of the external tanks for the North American Aviation X-15A-2.

I've identified a possible two other 'paint schemes' for the external tanks. Please can anyone else confirm that there are 3 paint schemes or more: The paint schemes I know of are the 'test tanks' (above), the external tanks without the 'colourful' markings (plain metal)  and the one below.

Thanks in advance for any help you provide. :)