Yes but no. In fact the syntax by itself is correct, it's the indentation that is wrong.
You can split long lines like this one in more than one line. But if you do so, you need to warn Ren'py/Python about it by creating an implicit block :
Code:
define NA = Character("Narrator",
color ="#e411bc",
who_font = "blahblah",
what_font = "blahblah",
what_size = 24)
In the code gave by
@Nickthegreek , all lines were at the same level of indentation, making them be five separated lines, instead of an implicit block of five lines (one for the header and four for the content).