From the Eye blog:
Stanley Morison became a director of Gollancz in 1928 and advised it on design for the next ten years. His legacy of yellow (Morgan’s Yellow Radiant) paper covers with black, red and magenta type continued for decades. (The copies shown here date from the early to mid-1930s.) Morison’s large headline fonts and pull quotes were radical at the time, especially when used with the then new Gill sans typeface.