Amber eye color in Neolithic Africa
There are two possibilities: First, that an individual develops a mutation de novo and is the first to carry it. 
When we talk about recessive expressed allels, than both parents need to have a copy of the allel, otherwise it will not show up in the kids. In this case a mixed population of siblings is to be expected (some carrying both recessive allels, some only one). 
However, its most likely, that the eye color at this time was brown. As far as I know, there has been no evidence so far from ancient DNA that this has been different. 

The oldest DNAfrom Europe, which has been analyzed and which showed a difference for the eye color comes from Spain (La Brana-Arintero site in Valdelugueros) and is about 7.000 years old. See this report about it. This individual is thought to have an "african" type of pigmentation but blue eyes. The original publication is called "Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European."

Another paper claims that the blue eye color comes from a mutation which occured in a gene called "OCA2" in the black sea region some 6-10.000 years ago. See here: "Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression"
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