The page does not say that the blue stone is a picture of a goddess.
Known. Blue colour is still on a stone from Sedeinga.
The stone was found at Sedeinga in Sudan, on the west bank of the Nile, about a hundred kilometres north of the third cataract. The burial ground there dates from the 7th century BC to the 4th century AD. This decorated stone, called a stele, was lying on its side. The colour left on it is mainly blue. That is rare, because colour on stones like this usually wears away.
The page does not say what is still argued.