fix Picker text color in DarkMode, tweak text size (#401)

* fix Picker text color in DarkMode, tweak text size

* review tweaks

React/Views/RCTPicker.m

@@ -23,16 +23,17 @@
 - (instancetype)initWithFrame:(CGRect)frame
 {
   if ((self = [super initWithFrame:frame])) {
-    _color = [RCTUIColor blackColor]; // TODO(OSS Candidate ISS#2710739)
 #if !TARGET_OS_OSX // TODO(macOS ISS#2323203)
+    _color = [RCTUIColor blackColor]; // TODO(OSS Candidate ISS#2710739)
     _font = [UIFont systemFontOfSize:21]; // TODO: selected title default should be 23.5
 #else // [TODO(macOS ISS#2323203)
-    _font = [UIFont systemFontOfSize:11];
+    _color = [NSColor labelColor];
+    _font = [NSFont systemFontOfSize:[NSFont systemFontSize]];
 #endif // ]TODO(macOS ISS#2323203)
     _selectedIndex = NSNotFound;
     _textAlign = NSTextAlignmentCenter;
     self.delegate = self;
-    
+
 #if TARGET_OS_OSX // [TODO(macOS ISS#2323203)
     self.controlSize = NSControlSizeRegular;
     self.editable = NO;