The epitaxial growth and characterization of multiple quantum well (MQW) optical modulators on GaP substrates is reported. The devices were fabricated using graded composition InGaP strain relieving buffer layers and strain-compensated InGaP MQWs. The devices operate in the 570-620 nm wavelength range with a maximum transmission change of 15% occurring at 594 nm for an applied bias of -10 V. The composition range required for the target wavelength range is near the indirect-direct crossover point for the InGaP material system and the corresponding effects on photoluminescence and absorption data is presented.