I would call Benjamin Moore Customer Support
1-855-724-6802 (855-Paint-02)

Explain that you have 10 gallons of Neon Celery paint purchased by mistake and ask them to help with formulating a color that is more muted that could be used by a charity like Habitat for Humanity.

If they can't figure out what to do with the color buy a sample of lily lavender and use an oral medicine syringe to mix equal amounts of lily lavendar and neon celery - should turn gray. Determine if you need a bit more of one or the other to get a nice shade of gray.

You will need to measure the amount of each paint so that the amount of colorant that needs to be added to the original color will be able to be measured.

If you post both formulas and the size of the sample and you know that you want the paint exactly 50/50 or 40/60 or 15/75 we can help do the math.