....interpolates between keyframes in a "circular" rather than "linear" manner?
Probably not explaining that very well: if you put two keyframes in the 3-way CC, and at one keyframe move the mids towards say cyan, and at the second keyframe move the mids towards say red, FCP will interpolate between them, as expected.
Except: what is NOT expected is that rather than plot a straight line between the two points on the Mids colour wheel going through the centre (as wanted - giving a reasonable result), it does a semi-circle (staying equidistant from the centre) from the start point round to the finish point, giving all sorts of undesired colour shifts between the two points.
Huh? Can anyone, more versed than I am in this, explain if there is a reason for this?
(PS: I know the workaround is to set lots more keyframes between the two, to constrain the point from wandering off course, but it's not very convenient, or fast.)
set lots more keyframes between the two
Or just one key frame with the pip in the middle, keeping other settings as they were?
I think the circular path is an 'intelligent labrador' thing, in that it's doing EXACTLY what it thinks it should do, even though a wider view would suspect otherwise. In other words, the hue is just a number between 0 and 'x' which cycles back to 0 again. This is represented on a disc rather than a wheel, which includes other parameters (gain in this case), so by keyframing the hue and not the gain, it travels ROUND the disk without daring to suggest or think that you may want to adjust the gain too.
A bit like the TomTom navigation experience, sometimes.
Thanks: I suspect you're right: the 3-way CC thinks in polar co-ordinates, not cartesian.