There is a bug with Graves' new auto attack animation. Not sure if items effect this or not, but the I'm going to say it could be influenced by either static shiv/rapid fire cannon. Graves' auto attacks will begin to flash a bright red/orange color every time he attacks after a certain amount of time.
Tysmin1 votesi'm pretty sure it is the statik shiv proc
ViciousSummoner1 votesThe source could possibly be from either one or it might be Graves' auto itself because I was 100% crit when this happened. Played a solo game about maybe 30 mins into the game maybe like 5-10 mins using 100% crit then it started to flash red/orange with every auto. I couldn't record it sadly because my minions destroyed the nexus before I had the chance.