Describe the bug
Can't deserialize page content when a paragraph is using the default background:

Newtonsoft.Json.JsonSerializationException: Error converting value "default_background" to type 'System.Nullable`1[Notion.Client.Color]'. Path 'paragraph.color', line 1, position 3000.
---> System.ArgumentException: Requested value 'default_background' was not found.
at Newtonsoft.Json.Utilities.EnumUtils.ParseEnum(Type enumType, NamingStrategy namingStrategy, String value, Boolean disallowNumber)
at Newtonsoft.Json.Converters.StringEnumConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)

I experienced it when working with templates. I'm not sure if it also happens for normal pages.

To Reproduce
Steps to reproduce the behavior:

1. Create a database
2. Create a template for new pages of the database
3. Add a few paragraphs without changing the background color
4. not sure what else needs to be done. (maybe something with custom layout?)
5. Load the page content via the .NET Api
6. There will be the above JsonSerializationException

Desktop:

• OS: Mac