All the text of these boxes are thoughts. This means that whatever the font is, the colour will always be grey.
If the text is told in a "story-like" way we use 'Felt' (standard size: 3,8pt - hex: #666666)
If the text isn't told in a 'story-like' way, then you may use 'Wildwords' (standard size: 2,9pt - hex: #555555).
Once you are experienced enough, you can play with other fonts for these boxes. But until then,
it's best to keep yourself to the basics.