^^ From your description, sounds like a combination of the dye/glaze settling into the uneven surface of the leather and now, with exposure to light, shows more color variation. Big question, does the look bother you? It sounds like it might be really pretty under light which would catch the surface variation.
Just scored an OH Mini Nikki for a steal at Funkylala with their code!!! Less than SS prices!!
It's due to arrive on Dec. 23!! Birdies and all!