Low-HF or HF-free processes for improving color stability of a Mn+4 doped phosphor of formula I include contacting the phosphor of formula I with a solution that contains hexafluorosilicic acid, and isolating a treated phosphor of formula I having improved color stability relative to an untreated phosphor of formula I Ax[MFy]:Mn+4  (I) wherein A is Li, Na, K, Rb, Cs, R4 or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; R is H, lower alkyl, or a combination thereof; x is the absolute value of the charge of the [MFy] ion; and y is 5, 6 or 7.