The Belgian Shepherd Dog is a breed of which the differents parts of the body are harmoniously proportioned. The body is well shaped, coherent and well balanced. The animal has style, type and distinction. It has remained a breed of runners. The shape of the muscles and the bones lends itself to a great mobility, a powerful jump and a start that is very rare for domesticated canines. The ears have the shape of a pointed triangle. Its muzzle is slender and without drooping lips, in other words with perfectly fitted lips. The big mouth is typical for the Belgian Shepherd Dog : when it opens its mouth, the jaws spread even further and the points where the lips come together are situated more at the back than with any other shepherd dog. We can notice the presence of a thick undercoat, the fluff, that protects against the cold and a coat that protects against the rain.
 

At the end of 1891 a large number of passionate fanciers got together in Brussels. Their aim was to research the best methods for making the brilliant physical and moral qualities of the native shepherd dog known and appreciated. On this occasion the 'Club du Chien de Berger Belge" was founded on 29 September 1891. At the General Meeting of 3 April 1892 the Club established the first standard of the breed. It divided the breed into three varieties without any distinction of colour :
                                       the long-haired
                                       the short-haired
                                       the rough-haired. 

In 1898 and 1899, it was decided to attribute a specific colour to each type of hair : black for the long-haired, fawn with black mask and overlay for the short-haired, dark ash grey for the rough-haired. The other colours were rejected. Why were the brindled, the pale fawn, the isabel-coloured and the black short-haired discouraged ?

In 1920, Charles Huge (the greatest belgian cynologist) wrote the following comments (quotes) concerning the colours of the Belgian Shepherd Dog :
" Although I am in favour of returning to our national shepherd breed all the grounds that used to belong him, I refuse to allow him colours that in living memory were never met with in the country. Never have we seen a chocolate Belgian Shepherd Dog or a mouse grey or black with intensive flames like the Doberman or the Beauceron. Fawn and black with traces of white on the chest and sometimes on the extremities constitute, in our opinion, the borders of the breed. But the fawn colour is varied and extensive as a range, and there we should not be exclusive and admit the entire range. The range varies from intensive auburn, sometimes with a lot of overlay like a fox, to the yellowish isabel-colour. Today we frequently see both in the same litter."

Relatively recent studies on the genetics of colours confirm the 1920 ideas of Charles Huge. Two pigments are responsible for the two colours of the Belgian Shepherd Dog: one is black (or aumelanic) and the other is fawn (or phaeomelanic). The isabel colour is the same as the "sable" with black overlay or commonly known as grey. The brindles (a mixture of black and fawn), who used to be overloaded with prizes have practically disappeared.

So, the varieties of the Belgian Shepherd Dog are the combination of the three types of hair and the two colours black and fawn (including sable). Some varieties received the name of a locality. 

Information: from www.Belgiandogs.org