I seem to get entirely too much of the colour cyan when using real colour blending.
As you can see in the first attached image, wet green plus wet blue results in cyan, and so does wet blue plus wet yellow. If I keep moving the brush, most of the time, the cyan will eventually disappear. With real colour blending switched off I get the familiar mushy grey from most combinations. The example is in watercolour but it also happens with the oil brush. It's possible to get pure cyan or pure white (depending on some random factor I haven't identified) by continuing to lay on paint in circles.
The second attached image shows a similar effect where the cyan doesn't immediately appear. It doesn't always turn out like this and different shades of red or green give different results. On the left is the starting situation and on the right is what happens when I continue laying on green paint. Sometimes the cyan is less pronounced, and sometimes I eventually get pure white. This also happens with watercolours, but is harder to see and easier if "Paper Wet" is enabled.
The easiest way for me to reproduce this is as follows:
0) select oil brush at 100% size
1a) either pick bright saturated blue blue,
1b) or pick a bright saturated red close to the top of the colour picker's range (i.e. on the violet side of red, not the yellow side)
2) paint a stroke somewhere on the canvas
3) pick a bright saturated green
4) paint a stroke next to the red or blue one
5) draw circles in the middle of the two strokes, if it doesn't quickly turn bright cyan, try again
I'm still on a Mac with Mac OS X 10.6. Oil brush settings appear to be 99% load, 8% thinners, 50% pressure, auto-clean on as of now.