It seems to be a bug in Adobe that editing the text styling (color, typeface, bold, italic, size, etc.) in a text box is difficult to do. This is what works for me:
1. Open your PDF in Acrobat. Make sure the Properties Bar is in view (Command-E).
2. Make a text box somewhere and fill it in with some text. Notice that the Properties Bar will let you change properties of the box but not the text inside the box, even if you have selected that text.
3. Save your file and quit Acrobat.
4. Reopen your file. You should be able to double-click on the text box you created, which will select the text within. The Properties Bar should now change to let you style the text. Future saves should let you keep doing this with new text boxes.
I hope this helps someone else; it took me forever to figure it out.