I buy purple and green. To step outside of my color comfort zone, I must SEE the project done in that colorway and then buy similar fabrics. I can imagine almost any project done in my favorites of purple and green! but cannot imagine it in another colorway.
Another suggestion is to go shopping with a friend. My GF loves neutrals, olivy greens, browns, etc. When I am with her, she helps me out of my rut and I do the same for her.