I've been using a toned mid-value canvas color as my starting base for about two years instead of white, and the difference in my painting process has been significant.

Painting on white creates a specific problem: white is the lightest value on the value scale, so everything you paint initially reads as a mid-tone or dark. You don't know if your lights are light enough until you fill in enough surrounding context. Starting from white means your lights are also surprises.

Starting from a mid-value grey or warm neutral: lights and darks are immediately readable against the base. You can assess value distribution from the first stroke. The composition and value structure reveal themselves earlier.

I use a warm medium grey (approximately HSB 30, 10, 65) for most subjects. For cold subjects or night scenes I use a cool mid grey. The base tone contributes to mood even after it's mostly painted over, because it shows through low-opacity strokes.