[Hologram]

I think you have misunderstood the Kahn photomicrograph. This is a 10 layer structure. What you interpret as silver being unevenly distributed is two layers as follows /overcoat/fast yellow/slow yellow/CLS layer/fast magenta/slow magenta/interlayer/fast cyan/slow cyan/AH/support.

Oops, now I can see it - silly me.

The fast layers are coarse grained and the slow layers are finer grained. That is what you see as inhomogeneity and that is what can be seen by the light as changing the nature of the layers.

And so the difference between coarse and fine grained layers, wouldn't it explain for the refractive index difference?