I-gene

 

The silver series.  This gene inhibit the colour in the individual hair. 
In an agouti hair it inhibit the golden colour which mesns that wher the bands in a non-silver is yellowish, in the silvervariant it is  white.  Gives the silver tabbies.
In the non-agouti it "pushes" the colour to end of the hair which gives a hair without colour at the lower part of the hairs.  Gives the smoke cats.

I am not fully aware of the genetic rules in the shaded and shell variant, but this gene gives the silver-shaded and the silver-tipped.

Silver dominates over non-silver, but there are a lot of overlaps, so sometimes the silver not alway is seen, but this effect do not make the silver ressecive - it is dominant.

[II] [Ii] [I-] is silver
[ii] is non-silver