Calico is a term that was originally used to describe a splash with red scattered throughout the plumage. The greys showing red were called by that term. THe someone started calling them tortise-shell. I've also heard calico used to describe a completely different colour pattern (I don't recall exactly what, but there was a photo). I only use calico in its original context: splash showing autosomal red throughout the plumage.
There is no standard as it is not a recognised variety, and different people mean different things by the term. THere is no gene for calico, unless you are referring to autosomal red.
If you want to know how well a particular bird meets the standard, you first have to decide based upon traits common to all silkies: type, feathering, comb, skin, toes. Then, if you want a non-recognised variety, decide whether you like his/her colouring or not. For breeding, without seeing photos of the birds in question, I cannot make any recommendations.
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