When Greta Thunberg delivered her “Our house is on fire” speech at Davos in 2019, she galvanised hundreds of thousands of school students to strike for the climate. The address was unique and potent in its urgency, but what did it look like in colour? What hues, textures and shapes could be ascribed to her words? One artist has sought to answer that very question, by transcribing Thunberg’s voice into a painting that will debut at Sotheby’s next month. Jack Coulter – who has synaesthesia, a neurological condition which blends the senses – has based his work, Future Generations, on a line in Thunberg’s speech which calls for the safeguarding…