I practice a lot, I like to get things just right and I usually use neutral colors and plain fabrics so I can truly see exactly what is happening with the shape and structure, it also forces quality and improvement in my handiwork when every stitch, pucker and fold is clearly visible.
Years ago there was this really amazing mill end fabric shop a few towns over, when you walked in, you never knew what you might find. There were first run proofs, rejected strike offs, misprints, factory remnants and discontinued full bolts at half price. In those days I was able to get so much natural duck cloth (canvas), cotton muslin, linen, and wool at an even deeper discount, because nobody wanted those plain fabrics. Most of the quilters and sewists that were shopping along side me, were coming in for the more colorful quilting cottons & fashion prints.
Over the years, the side effect of always having bulk neutrals on hand was that it became my color and fabric of choice. Basic, unfussy, perfection.