I'm using the Personalization feature in the WYSIWYG editor in attempt to render the value of a Custom Constituent field. I'm not able to see the custom field in the list.
If it's a Boolean field (Yes/No, True/False) then you won't be able to render the value of this field using Personalization. Instead, click the "If" icon (Conditionals).
Click "If" in the WYSIWYG Editor
Click Additional Information
Click the name of your Boolean field
Select true or false
The selection of true or false will determine what should be displayed depending on the field's value. For example, if you selected true, then you can enter the text that will display if the value is true and enter the text to display if it's not true (false or blank). Vise-versa, if you selected false, then you'll enter the text to display if the value is false and what text to display if the value is not false (true or blank).