Here I have a good photo of a dog with agouti genotype. Although it's a different breed (but with similar coat), you can see very well the changing in pigment type. Because of the permanent hair growth the dark tipps are (almost) grown out. When growing further on the black band will appear at the tipps and a new black band will be at the base of the hair.
Gene “aw” (sometimes it’s denoted as “ag”) – this is the very gene above, the gene of the agouti colour (grey-wolf, wild boar, pepper and solt are the same colours). Agouti is formed in the following way: as soon as the new hair begin growing, the maximum quantity of the black pigment concentrates in them. Later the pigment producing decreases and we can watch less concentration of the pigment granules on the length of the hair. But in this period the mechanism of the red pigmen producing has already started and under these changes’ influence the colour in the hair smoothly turns into the red colour. When the red pigment granules’ producing runs up to their maximum and the colour of the next zone becomes almost white then the black pigment producing mechanism starts again. After the light area there appears the dark one. Thus dark and light areas of the hair take turns.