Here are two projects involving the geometrical-constructive art of Piet Mondrian, one of my preferred artists, the golden ratio and ϕ. For this purpose, I used the same color palette favored by Mondrian: yellow, red, blue, black and gray.
Mondrian meets Pythagoras and Fibonacci
In the first project, I used squares, that are proportional to each other by the golden ratio or ϕ, to prove the Pythagorean theorem as shown in the Zhoubi Suanjing (or Chou Pei Suan Ching – 周髀算經), one of the oldest Chinese mathematical texts (circa b.c. 200).
The side of medium white square / the side of small black square = golden ratio, which is the limit of the ratio of consecutive Fibonacci numbers… 
Below is how the finalized op art work looks like.
It looks great featured on T-shirts and apparels…
This geometric art work is available on T-shirts and posters from my online store.
Mondrian meets Fibonacci
In the second project, I used the well-known Fibonacci spiral, which approximates the golden spiral using quarter-circle arcs inscribed in squares of integer Fibonacci-number side (0, 1, 1, 2, 3, 5, 8, 13, 21, 34, and so forth).
Below is how the finalized op art work looks like.
Again, the design looks great featured on T-shirts…
This geometric art work is available on T-shirts and posters from my online store.