What you are failing to grasp is that in the shaded area there will be both black and white colour flecks as with populations in this area , if species change is happening then there should be both types in various ratios at all times
Not flecks... its a pure blend.
You are not looking at Dalmations.
And it is best explained as changes in allele frequencies over time...those alleles being the allele for black and the allele for white.
Each individual has several copies.... say AAAAAA for black and aaaaaa for white. These genes are called co-dominant because they both express equally in the individual.
So an individual with AaAaAa would be the very middle tone of grey.
Start with a population that is AAAAAA. (lets say that AAAAAA can't reproduce with aaaaaa you can't have more than one case difference to reproduce)
one individual has a mutation that makes it just a bit lighter than the rest AaAAAA.
This mutation somehow makes the lighter individual just a bit more likely to reproduce... over time their descendants make up the majority of the population.
Just by the way genetics works eventually one of those descendants is born AaAaAA.
Being a little lighter than the rest, this one too has a better chance at having lots of kids.
Over time this ones descendants now dominate in the population...
And again... AaAaAa...
And again... aaAaAa...
and again... aaaaAa...
and finally... aaaaaa... Now a genuinely white individual is born. It being lighter than the rest can reproduce a bit more successfully and over time it's descendants dominate the population.
Yes there very well may be some AAAAAA individuals living somewhere... but they are now so different from the aaaaa population that they can't interbreed. Thus you would now have a "black species" and a "white species".
wa:do
ps. an allele is a gene that codes for a specific trait. (in this case color)