I found an Oil Painting without Solvents PDF at the Art Spectrum website. It is rather general but does have some useful information. In particular I found the bit about Spectrum Clear Oil Paint interesting:

Spectrum Clear Oil Paint is a product well worth exploring. It is formulated as an oil paint, but without coloured pigments. With Clear Oil the integrity of each brush stroke is retained, which is not the case with most mediums which tend to level or smooth out brush strokes. It can, however, be considered a medium because of the effects it helps create. Clear Oil Paint can reduce colours to pale tints without the use of whites or mediums.

• Tremendous depth of colour is possible by painting wet into wet or in thin glazes
• Oil colours can be extended without loss of brilliance or structure
• Opaque colours can be made transparent
• As many Art Spectrum colours are transparent, try making use of this quality by using Clear Oil Paint instead of white.

I experimented with some the other night and it did seem very useful for diluting paint in a similar manner to a medium. It is quite a free flowing consistency so spreads onto the canvas very nicely. As stated above it is a nice alternative to mixing paint with white. It would be very nice for spreading onto the canvas and then painting into it wet on wet. I just had a dob of the spectrum clear paint on my palette and would just grab a bit every time I wanted to spread some colour out onto the canvas thinly.