'ashy' originates from English, specifically from the word 'ash' with the adjectival suffix '-y', where 'ash' meant 'the powdery residue left after burning' (and also referred to the ash tree).

'ash' comes from Old English 'æsc' (and Proto-Germanic '*askaz'), and the adjective was formed by adding an Old English/Germanic adjectival suffix (historically -ig, evolving to modern -y), producing Middle English forms that led to modern 'ashy'.

Initially it referred to something covered with or like 'ash'; over time it has retained that core meaning (pale or gray like ash) and also developed extended informal senses such as describing dry, powdery skin.