In Calls in the US, a snowy Call is a call that has two copies of the li^h harlequin gene but otherwise has the genetics of a regular gray Call. Spot is one copy of li^h, and then also one copy of li Light Phase. The two interact to form the lighter Spot color.
I'm thinking then that your Abacot is a double dose of harlequin. Or are you saying that it's a totally separate new gene just called ACG? If so, which locus is it at on the chromosome? Is it at the locus of the other color phase genes?
What is the genotype of your Abacot and the genotype of your Spot? If you can tell me that, then I'll know for sure which colors are the same 

 Like this, this is the genotype of a gray Call drake; can you write this out for your Abacot and Spot?
M+M+ Li+Li+ e+e+ bl+bl+ C+C+ B+B+ r+r+ D+D+ Bu+Bu+
The picture of your drake looks to me just like a snowy here in the US, as does the hen. The picture on the magazine cover looks like what we call Spot here. So I'm thinking what we call Spot you call Silver, and what we call Snowy you call Abacot. Different names for the same colors.
It appears I just had the color names wrong, since everyone usually says that silver in the UK is snowy here in US, or at least that's what I've always read. It seems instead that it's actually Abacot that is analogous to Snowy.
Here's a genetics calculator that has all the colors on them, though the names might be different from what you call them since the creator of the calculator is Dutch. To me, Abacot like you're describing falls under snowy. Silver falls under Spot. Or perhaps 'silver spot' which is regular spot but also dusky.
http://kippenjungle.nl/kruisingEend.html