To see through rose-coloured spectacles

 
To see things through rose-coloured spectacles or rose-coloured glasses means to view events and people positively seeing only their good points; to have an attitude of cheerfulness and optimism; to see everything in a favorable and pleasant light; to have unmitigated optimism.

Mum often talked about people seeing things through rose-coloured spectacles. She had heard he expression as a young child at school in the 1910s and had loved the idea so much she was still amused by it in her nineties. In fact, the term began to be used in the 1850s and is first found in print in 1861 *, when it appears in ‘Tom Brown at Oxford’ by Thomas Hughes. “Oxford was a sort of Utopia to the Captain . . . He continued to behold towers, and quadrangles, and chapels, through rose-colored spectacles.”

(* See amendment in comments)

A similar 20th-century idiom is to ‘see the glass as being half full not half empty.’