As kinda the opposite of onebulb's comment below, for my use case I needed the sprites to transition between being tinted when speaking but left fully untouched at baseline. My modification ended up looking like the following:
if is_talking: # Apply the talking transformation
trans.matrixcolor = SaturationMatrix(1.0 + (curr_ease * sat_change)) * BrightnessMatrix(0 + curr_ease * bright_change)
else: # Apply the not-talking transformation
trans.matrixcolor = SaturationMatrix(1.0 + ((1 - curr_ease) * sat_change)) * BrightnessMatrix((1 - curr_ease) * bright_change)