Mix white sugar, brown sugar, and water in a medium saucepan. Bring to a boil and simmer for about 3-5 minutes. Do not stir at this time. Remove from heat.
Stir in the ube flavoring and vanilla. Let it cool for at least 10 minutes before serving. Store in an airtight container in the fridge.
Notes
Store the syrup in an airtight container in the refrigerator for up to a month.
DO NOT STIR while the syrup is still simmering to avoid crystallization of the sugar.