So this is weird.... I have a scene with IBL plus two colored spotlights:

Gray is the IBL, blue and red are spotlights. The lights are actually changing from animation frame to frame, not sure whether that's relevant, but this shows the lights from the frame shown in the renders below. (The same problem happens in the other frames, I just picked this one as an example.)

Quite often, when I first render the frame, especially after newly loading the file, it comes out with relatively white lighting (there is a little color from the IBL, but mostly white):

Simply repeating the render doesn't change anything. But, if I then select the light and open the color picker, and make the tiniest possible change (basically I'm trying to make Poser think I changed something without anything being different), and re-render with exactly the same settings, I get colored lighting, and you can see we're not talking about a subtle difference here:

Note that I have to do this for both lights. If I only touch one of them, that light is in color but the other one remains white.

I'm not sure what's really going on here. It's possible the IBL is being omitted in the second render (maybe like the preview there is a limit on how many lights are displayed at once?), but I think the difference is just that the spotlights are showing up as white in the first render. The lighting direction seems consistent.

I did some tests and the result is the same regardless of CPU rendering, GPU, or Optix. (Although I also had some issues with GPU and CPU renders never stopping, in 12.0.306. Not that I want to ever use them, I am already spoiled by the speed of Optix.) Also did not matter whether I used a transparent background or not. I am using Superfly though.

I started seeing this in 12.0.289, but since 12.0.306 just came out, I tested it as well, and get the same result.

Anyone else seeing oddities with lights that are not white? Inconsistent results? Lighting appears whiter or brighter than expected?

IIRC, IBL does not work in Superfly. Double-check the manual on this subject. There is a list of features that is not supported by Superfly.

Superfly doesn't support ambient occlusion for lights, or atmosphere strength, or some shader nodes (it's possible the images I assigned to the lights aren't working, I'll have to test that). But I don't see anything to suggest you can't use IBL at all, I don't think that's correct. I have AO unchecked in the light settings in any case.

The lights that are being wonky here are spotlights, though.