I messed about with an UA and a meta-alloy seed yesterday. Nothing happened, even when I got them to touch each other.
The most interesting observation is how the objects reflect light. This was in daylight (not quit noon) conditions.
The UA is very bright. Almost white. The meta-alloy is quite dark, even in the sunlight.
The grey bits on the Meta-Alloy and the darkest bits on the UA head (the bits between the ox-head markings) seem like the same material. They still reflect light very differently.
Probably just settings on the 3D models. They are most likely optimized for different light environments.
Edit: I thought I was able to spot a barnacle from 9km yesterday, but it turned out to be Commander Darwins shiny white Cutter. It was beautiful in the sunlight.
The barnacle became visible for me at about 3km.