@tsarstepan,
yeah thats probably it, I seen several of his works including those that look like Edw Hicks primitive style , like Peaceabl Kingdom (the work that defined the Quaker church in the US during the early days of the republic), and most of both their works were not that brightly bluish with very strong values . Rousseau originals at museums were often more warm toned. probably due to age. Maybe all those others qre attempts at catching what the original would look like when he painted it.