In many plants, purplish or reddish color of leaves can be from Phosphorus deficiency, but I don't recall having heard that discussed about mangos.
Severe Magnesium deficiency usually produces a bright orange color, sometimes with scattered spots of red. Early Magnesium deficiency shows interveinal chlorosis in the mid and tip areas of the leaf, while the base of the leaf remains green, often in a v-shape of green.