Hello cultmia ,
Please follow the below given link to create color swatches for the product
If you find Callback function in Brooklyn theme as per give doc. then you can on find because in Brooklyn theme callback not define with "selectCallback" function.
You can find this code in Asset->theme.js->find "if (variant)" where you can see function.
This variants generated by theme and you can find on section->product-template.liquid->search form and within form you can find variants html code.
But This variants may be auto hide when you apply swatches but dont know how's you implemented but you can follow this.