I think it is important to stress that both, color _and_ shape should be visible distinctive, and as you say it is important that the color palette is chosen in a way that even if the color does not stand out for a the color-blind person, the contrast stays visible.
Making everything monochrome is surly not more accessible, because there sure are people who find it easier to distinguish by color than shape.
Making everything monochrome is surly not more accessible, because there sure are people who find it easier to distinguish by color than shape.