The leader all in white is the chief. All the other leaders are wearing some other color, but that's how you tell the chief apart from the other leaders.
The reading is the same as 白, which is included in this kanji. The other reading is お, and it's like the honorific 御, in a way. You'd want to be polite to someone who is the chief ______, right? That's why it could be お, too.