Chromatic effects of dynamic irises?

I've got a new PT-AE8000U and am wondering if anyone who is better acquainted with optics can help explain something I'm seeing.

When I first set up the projector, the image looked great but after going through the menus and making various settings changes I noticed a blue fringe or bloom coming off the bottom of white pixels. I'm pretty sure it is not outright misconvergence, because single pixel white horizontal lines still appear white. It's just that if there are white pixels below, there's a minor blue shadow cast upon it. Black pixels do not cast a blue shadow over white pixels below.

After a bit more futzing with settings, I found that turning off the dynamic iris noticeably reduces this blue fringe. At the same time, I also notice that turning off dynamic iris appears to make blues richer, for example in the menus.

My understanding is that the iris opens and closes to increase or decrease the overall amount of light coming out the projector. But does it make any sense for the iris to be affecting the characteristics of just blue? If so, what exactly is happening?

TIA.

Thanks for the answer Kelvin. You're saying the dynamic iris function actually modifies parameters in the video processing pipeline? It's not limited to physical iris aperture changes? That seems silly to me.

I guess that would explain the difference in blue saturation. But still not sure if that accounts for the difference in blue bloom/fringe. The bloom/fringe actually goes down (better pq) as the blue saturation increases (also better pq).

In any case, pq looks better with dynamic iris turned off. I will leave it that way.