when you say black or silver are you simply refering to color or materiel? I never cared for Alumium nipples unless you were building race or TT wheels. therefore I always used silver or more exactly the chromed brass nipples. if the bike is well cared for corrosion or rust should never be much of an issue.
as for mixing and matching brands as long as you are threading 14ga nipples on to 14ga spokes brand should not matter
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk