I've been breeding pokemon for the appropriate IVs but for some reason, trying to breed a poliwag with HP Grass feels impossible. The IV spread is supposed to be 30/31/31/30/31/31

and even though I have the 4 perfect IVs on the stats I need, it continues to show up as dark. I never had this when breeding my Jolteon for HP Ice or my Espeon for HP Fire. Is there something I'm fucking up?