Final answer:
The day dress designed by Yves Saint Laurent in 1965 was inspired by the artist Piet Mondrian and the movement De Stijl, a Dutch art movement focused on geometric shapes and primary colors.
Step-by-step explanation:
The day dress designed by Yves Saint Laurent in 1965 was inspired by the artist Piet Mondrian and the movement De Stijl.
Piet Mondrian was a Dutch painter associated with the De Stijl movement, which sought to create art based on geometric shapes and primary colors. His compositions consisted of grids and lines that divided the canvas into abstract forms. Yves Saint Laurent incorporated these geometric elements and primary colors in his dress design, reflecting the influence of Mondrian's art.