Find a familiar base
Begin with colours you already reach for. A useful palette can be built from what feels natural, rather than what an outfit is supposed to contain.
Let texture do some work
Close colours can feel distinct when their surfaces catch light differently. A flatter base and a more textured layer can bring interest without another strong colour.
Choose a small contrast
Try a small change at the collar, cuff or shoe. The contrast does not need to become the focal point of every part of the outfit.