The Champagne gene is the newest colour available to mini breeders.  
At least one parent must be champagne to get a champagne foal.
It has the ability to dilute both black and red pigment. If it is present it will always display itself physically  and it will lighten or dilute a coat colour (except on a white horse - ie, extreme sabino, grey etc). 

• Champagne foals are born with a dark coat that lightens with age.
• Champagne horses are born with blue eyes, usually going through several changes as the foal matures. They start blue, go greenish, then hazel and end up amber. Some horses retain the blue or green colour.
• All Champagne horses are born with pink skin that usually darkens to a purplish brown with maturity. 
• Freckled skin is very common. This can be found around the eyes, muzzle, under the tail, and the sheath/udder areas. 
• Champagne horses MAY have a metallic glow or sheen to it's coat. Not all Champagne horses have this glow and it can occur in horses that are not Champagne.  
• Another physical characteristic that can occur with the Champagne colour is reverse dappling. But again, this is also occurs in horses that are not Champagne.

There are 4 different shades of Champagne.  

Gold  (chestnut + champagne)
Amber  (bay + champagne)
Classic  (black + champagne)
Sable (Seal brown + champagne)

As well as all the combinations you can have by mixing dilution colours, patterns etc - see also Mixed dilutes for examples of champagnes.

More information on Champagnes can be found on the International Champagne Horse Registry web site.