Splat usually washes out in about 6 weeks, but it may wash out more quickly if your hair is not bleached. It will also appear more subtle on unbleached hair, so it might look like it's completely gone sooner than it would otherwise.
How long does splat no bleach kit last?
4-6 weeks
Can you reuse splat bleach?
Can I re-use my Splat hair color that's been opened for a couple months now? Only if you opened the colour and the developer and didn't mix them together. If you mixed the two together then it loses its effectiveness. In some cases, those bottles may explode after a bit if you let it sit (mixed).