Adjust syntax highlighting colours

Blue is a little dark in some dark themes, meaning the contrast is
sometimes too low.

Closes #108

src/style.rs

@@ -195,8 +195,8 @@ pub fn color_positions(is_lhs: bool, positions: &[MatchedPos]) -> Vec<(SingleLin
         let style = match pos.kind {
             MatchKind::Unchanged { highlight, .. } => Style {
                 foreground: match highlight {
-                    TokenKind::Atom(AtomKind::String) => Color::Cyan,
+                    TokenKind::Atom(AtomKind::String) => Color::Magenta,
-                    TokenKind::Atom(AtomKind::Comment) => Color::Blue,
+                    TokenKind::Atom(AtomKind::Comment) => Color::Cyan,
                     _ => Color::White,
                 },
                 background: None,