The present invention provides a decolorized red phosphorus composition capable of inhibiting coloring in dark red peculiar to red phosphorus even when kneaded with a resin or the like, modified red phosphorus used for the decolorized red phosphorus composition and a production method therefor, and a flame-retardant polymer composition using the decolorized red phosphorus composition. The modified red phosphorus includes red phosphorus particles (A) whose surfaces are coated with a modified resin film (F) containing white particles (B) having a whiteness of 70 or more, color particles (C) having a hue H of 30 to 80 in the Munsell color-system hue circle, and a binder resin (D). The decolorized red phosphorus composition includes a mixed powder containing the modified red phosphorus and white particles (B) having a whiteness of 70 or more. The flame-retardant polymer composition contains the decolorized red phosphorus composition and a polymer compound (I).