It sounds to me like your formula has broken the base and exposed warmth in between, especially as the picture shows some parts have turned ashy which I imagine are the highlights. The issue is that even with 1.9%, Illumina is still a permanent colour and will always break the base, with the only way to reduce the chances of it doing so is mixing Illumina as a glossing mix as it reduces the alkalinity but sadly it's just inevitable on highlights. Hopefully over time the warmth will die down as the tones fade, especially as it will definitely look more obvious next to the cool blonde areas, so in the meantime if its a big issue your only options are either to tone the hair down darker, or lift up the warmer pieces so they can be toned along with the blonde. For highlights I usually prefer to stick with Colour Touch or Shinefinity as breaking the base is a lot less likely. Just remember if you have to/really want to use Illumina or Koleston for toning highlights then you'd be best to mix it in the glossing mix to reduce the alkalinity as in that mix most of the time it's not strong enough to break the base.