I've got to post about this. In brief, if you want to make washes or filters you want a "student grade" oil paint of which Abteilung is simply the most expensive. Reeves at Micheal's or Blicks sells for about $15 for 12 little tubes and it'll make a lot of washes. Whoever said buy extra white is right.
If you want to mix paint then I'd stick with real artist grade oils. Artist grade oils have "pigments" combined with linseed oil. The pigments can be chemical or natural: some are extremely expensive, others much less. (Let me tell you: if you get a series 4 blue or red from a good maker, the color will explode - it's really something. Also enough to last a modeler about five lifetimes.) Luckily artist grade white is cheap. Student grade have oils that are mixed with "hues", not pigments. The difference, simply put, is that student grade oils have paint inside the paint. Artist oils are almost closer to using weathering pigments. The reason artists buy artist grade (assuming they can afford it) is that the pigments are more powerful and thus you get better coverage and, if you want it, truer and deeper colors. The other reason is that pigments mix together very well. Hues don't. Try mixing modeling acrylics together - if you don't know what you're doing you'll end up with something muddy really fast. Much less likely to happen with pigment based paints.
Anyway, if you want washes get a student grade oil - there are lots of brands. If you want to mix paints, and painting figures might well reward that, get artist grade primes (red, yellow, blue, green [green's cheating, but do it] a black and a big tube of white. If you're lazy, as suggested above, something like burnt umber is very nice. Color mixing is an absolute gas and is an art of its own. Use only very small amounts - dole it out with a toothpick. If you're painting with an oil, watch thinner use. There are "mediums" available that are also oil based to alter the nature of the paint, (change its consistency, make it matte, satin, gloss: about anything really) but too much thinner will break down the chemical glue that holds the paint together. Talk to an art shop guy about thinners. I prefer mineral spirits but know some artists that insist on turpentine.
Eric