Been using my K500 for 3 months without any problems. Today took some shots of a cosplay event at Downtown East. The rain stop & the skies overcast. Took about 50 shots & suddenly some pics got reddish/cyan colour cast intermittenly. I tried changing iso from 200 to 100, shutter speed & F stop & still it happen once every few shots. Using my Pentax 16-50mm on manual mode & a Metz flashgun also on manual with 1/4 power ratio with diffuser. The affected pics can be edited easily but what caused this colour cast? Hope it's not the camera problem