Blanche Gladys Colston, Lady Roundway (née du Bois Duddell, born 1879) was a British tennis player.

She was a runner-up at the British Covered Court Championships in 1902 and 1922, twenty years apart.

She defeated Lenglen in the mixed doubles finals at both of those tournaments, partnering with Triple World Champion Anthony Wilding in the latter event, making her one of the few players to defeat Lenglen in multiple matches.

Her father was a property owner who became wealthy doing business in Hong Kong.

[3] She had an older brother William Duddell who was a physicist and inventor.