When trying to build an animation in Poser, I sometimes try to change the intensity and colour of the lighting, only to find that somewhere along the way between key frames, my lights go from, say, a warm beige to an intensely bright white or else pitch black. Nothing in the keyframes tells me why this happens, and if I set up additional keyframes to compensate, all that happens is the white (or black) moves somewhere else inbetween. Arrrggghhhh! Any one have any idea what's happening here? The manual doesn't address this at all.

This may be a result of spline interpolation between keyframes. Too many keyframes too close to eachother will result in some wacky curves between points. Select the light, open your Graph tool and select the Intensity channel. Here you can see a line graph of the value of the intesity over time. You may be able to fix this by spreading out you keyframes and making the values more subtle at each keyframe, or by changing your keyframes from spline to linear interpolation.

Or use "break spline"