The fuses (tips) are steel colored but the actual warheads are color-coded for identification:
M151 HE - Olive drab with yellow markings
M156 White Phosphorus - Light green with a single yellow band and markings
M247 HE Dual Purpose - Black with yellow markings
M257 Illumination - OD with white markings
M259 Smoke - Lt green with red markings
M261 HE Multi-purpose submunition - OD with single yellow band and markings
WDU-4A/A Anti-personnel (flechette round) - OD with white markings