AVOID! So about a week into my balayage my hair got extremely frizzy and irreversibly damaged (imagine straw). I came back to Sparks for Keratin and Olaplex treatment to save my hair but it didn't work, even after months of intensive treatment (hair mask, specialty shampoo & conditioner etc).
That was because the Spark' s hairstylist lightened up my hair in one session. Later on after speaking to several experienced hairstylists, I found out that NO knowledgeable stylist would EVER lighten dark hair for balayage in one session; it always take multiple sessions before the final look is achieved to ensure your hair remain healthy and not damaged.
I ended up having to cut all of the balayage part because they got unimaginably tangled to the point no Sephora expensive hair cream/detangler/hair mask or fancy comb could detangle them.
Please choose another salon if you want to have a balayage and you don't want to end up like me having to cut most of your hair or stuck with extremely damaged, dry, frizzy and tangled hair.
I would suggest Lisa Thi Dinh - the wait is long but it's worth it in the long term considering that you save a lot of money on fancy hair products to reverse the damage and their coloring style looks superiorly better/more flattering than at Sparks.