The terms denoting BLACK and WHITE appear in (almost) all languages. In some cases, they are the only colour terms the language has and in this case they refer not only to black and white but to different shades of grey and to the presence or absence of light as well, thus having a much wider semantic scope.
The inventory of basic colour terms in Czech and Finnish contains more expressions than these two, however in toponyms the most frequent colour terms are BLACK and WHITE which at the same time show the qualities of macrocolours. Despite the differences in the landscape and language, the colour terms in toponyms of both areas tend to show certain similarities, e.g. the wider semantics of a macrocolour, or similar ways when explaining these names.
These explanations seem to be reflecting more the naming motivation than being a "naive" folk etymology made up later. This actually testifies about the universality of colour perception and conception which is more permanent and obvious in toponyms than in other appellatives, regardless of the language.