Odd colour mixes that work ...

Yes, PR.108 is a single pigment - while the actual colour varies between each of those variants: I did look this up the other day, but have already forgotten the detailed answer (my excuse is that I've spent the day playing with gouache, and trying to draw a late friend from memory: pointless of course, you'd need a photographic memory which I haven't got; and all that rapidly removed my latest bit of research from my mind, or corrupted my mental files.....): but I digress... Cadmium Red - available as Light or Pale, plain Cad Red, and Cad Red Deep, has to contain PR.108, or can't be called Cadmium Red at all.  Hue colours - you probably know this - may be labelled as Cadmium Red (Hue): but won't contain the genuine Cadmium pigment.  So far so good.  The quantity of the pigment added to the binder is the answer here - apparently.  Making paint is an expert science - paint-makers have to understand precise quantities in order to produce consistent colour, and it's not that unusual for a single pigment paint to take different tones - the same is true for example of Cobalt Blue, and Cobalt Blue Deep; Cerulean Blue - which varies a lot between different makers - will still be PB.35, however different it may look.  Its 'Hue' varieties are usually pthalo blue in much reduced strength, and nowhere near as subtle; there's a very large difference between what Daler-Rowney call it - George Rowney was the frst to introduce the paint (in 1805, I think) and called it 'coeruleum' - and, say, Rembrandt Cerulean: but - it's the same pigment.   And on it goes.  I like to use single-pigment colours, though am not fanatical about it, because you can mix just about anything with them.  The Cobalts and Cadmiums (Cerulean is Cobalt Stannate) are among the most stable and lightfast pigments we have.  Digressing further - the EU was considering banning cadmium paints at one point, as they had more or less made lead paint impossible to find (for rather better reasons - lead is very toxic; but they went a bit far).  SO - paint-makers, and several artists - myself included - submitted evidence on use of the cadmiums to the EU, and it agreed not to ban them; some companies seem to be anticipating bureaucracy taking another bite at this, and are marketing 'cadmium free' paint; this is a stupid bit of marketing, because it contributes to the idea that the way artists use cadmium paint may be, in that wonderfully elastic word, 'toxic'.  I wish we'd managed to mount a similarly robust defence of lead whites - they did in the USA and won their case.  We had to put up with severe restrictions ..... I could run on longer to explain why lead white paints are nonetheless still available, but suffice to say that they are, if you know where to look.   The metallic-based paints are among the painter's best friends - all of them have come under pressure from those concerned about their toxicity, all need to be used with care and consciousness of studio/home hygiene.  We do need to watch out for threats to their continued use. All this, and you only asked about PR108!  

The medium with the water solubles - a bit of a misnomer, they're miscible rather that water soluble, but it's not worth getting pedantic about!  It just means that water can be mixed with modified oils, but the oils aren't soluble in water - eg, can't be re-worked once dry.  The medium is, in the case of W & N's Artisan range, and presumably in Cobra's, a modified Linseed oil.  I don't know how the oil is modified - that's supposed to be a trade secret, and I probably wouldn't understand it anyway.  Linseed oil is the best medium, at least for the first layers; Walnut oil is fine too, poppy oil - takes an age to dry.  Thinners, though - yes, I do understand that people are very wary of Turpentine, and probably should be just as wary of the various low-odour alternatives, including Zest-it: none is entirely hazard free.  I also understand that water miscible paint is a lot easier to clean up afterwards - but you don't have to use any thinners at all: that's too involved and long a subject to go into in what is just a reply on a thread, but plenty of artists use just a minimum of oil to loosen up the paint, mash it with a palette knife to produce a more fluid consistency, don't use Liquin or other alkyd mediums, and never use solvents.  I always have a bottle of Turps tucked away, but very rarely use it.  If anybody wants a fuller explanation of this, I'll be happy to write a gurt long piece in another thread - but for now, this is just a "just sayin' " comment.