Sky blue
From Tardis Wiki, the free Doctor Who reference
Sky is a light form of blue named after the sky.
The Eleventh Doctor wore a sky blue shirt up to his death. (TV: The Bells of Saint John, The Day of the Doctor, The Time of the Doctor, etc)
Diane Holmes wore a sky blue shirt with her sleeves rolled up when adapting to the 21st century. (TV: Out of Time)
