I try to explain what "light" Columbian is all about.
Their is the groundcolor which is determined by the e-allele.
In Silkies you can have a Columbian on eb (Asiatic Partridge = grayish undercolor) or on eWh (Wheaten = colored undercolor).
The light Columbian is a Silver (S) based bird (a buff Columbian is a gold (s+) based bird).
To become the Columbian pattern you need the Columbia black-pigment restrictor gene (Co).
Each gene have 2 alleles (example Co/Co = 2 dosis Columbian or Co/co+ = 1 dosis Columbian) except for the sex-linked genes (example S/S = 2 dosis Silver) here the females have 1 "full" allel and a "shriveled" allel (example S/- = 1 dosis Silver).
I not want to go to deep into the color-genetics but a basic knowledge is much handy.
To have a Light Columbian Silkie this bird need to have the following color-genes (I will write only the pure color-genes recipe).
1. groundcolor : eb/eb or eWh/eWh
2. based on Silver : males = S/S, females S/-
3. black-pigment restrictor : Co/Co
So you can see a Light Columbian Silkie can be a Asiatic Partridge based on Silver with a black-pigment restrictor gene.