Here you can see that in the bead I reduced, the colour is much darker. I'm not sure if this is because it struck in the reduction flame or if reducing it actually darkened the colour. Putting silver on Light Umber also made it a dark brownish green.
In the leftmost bead, you can see that silver turns a greyish colour and stays more or less in place on top of Light Umber, similarly to how it behaves with Ivory. Reduced and encased, the silver turns blue.
I am pretty sure that this cracking was the result of me having a rod of old Precision 104 Diamond Clear mixed in with my clear shorts, and not from putting silver on Light Umber, but the bead I put silver leaf on top of cracked in a really odd way. It's clearly a compatibility crack, because of how weirdly jagged and around the widest part of the bead it is, and dicey clear is the only thing I can think of that could have caused this.
Light Umber goes dark in beads with silver glass, too. I think it's a great base colour for silver glasses - the reduction colours pop, and the striking silver glass got beautiful purples even if I wasn't patient enough to properly develop the colour.
With Copper Green, the edges of whichever colour is used in smaller quantity get dark, but the reaction is mild. Light Umber separates slightly on top of Copper Green and Copper Green spreads on top of Light Umber.
There are no obvious reactions between Light Umber and Opal Yellow, Ivory, or Peace. There is a slight separation of Light Umber on top of Opal Yellow and Peace, but nothing dramatic.