Fixes backButton.color issue - #4150

lib/ios/ReactNativeNavigationTests/UINavigationController+RNNOptionsTest.m

+#import <XCTest/XCTest.h>
+#import "UINavigationController+RNNOptions.h"
+
+@interface UINavigationController_RNNOptionsTest : XCTestCase
+
+@end
+
+@implementation UINavigationController_RNNOptionsTest
+
+- (void)setUp {
+    [super setUp];
+}
+
+- (void)testSetBackButtonIcon_withColor_shouldSetColor {
+	UIViewController* viewController = [UIViewController new];
+	UINavigationController* nav = [[UINavigationController alloc] initWithRootViewController:viewController];
+	UIColor* color = [UIColor blackColor];
+	
+	[nav rnn_setBackButtonIcon:nil withColor:color title:nil];
+	XCTAssertEqual(color, viewController.navigationItem.backBarButtonItem.tintColor);
+}
+
+- (void)testSetBackButtonIcon_withColor_shouldSetTitle {
+	UIViewController* viewController = [UIViewController new];
+	UINavigationController* nav = [[UINavigationController alloc] initWithRootViewController:viewController];
+	NSString* title = @"Title";
+	
+	[nav rnn_setBackButtonIcon:nil withColor:nil title:title];
+	XCTAssertEqual(title, viewController.navigationItem.backBarButtonItem.title);
+}
+
+- (void)testSetBackButtonIcon_withColor_shouldSetIcon {
+	UIViewController* viewController = [UIViewController new];
+	UINavigationController* nav = [[UINavigationController alloc] initWithRootViewController:viewController];
+	UIImage* icon = [UIImage new];
+	
+	[nav rnn_setBackButtonIcon:icon withColor:nil title:nil];
+	XCTAssertEqual(icon, viewController.navigationItem.backBarButtonItem.image);
+}
+
+- (void)testSetBackButtonIcon_shouldSetTitleOnPreviousViewControllerIfExists {
+	UIViewController* viewController = [UIViewController new];
+	UIViewController* viewController2 = [UIViewController new];
+	UINavigationController* nav = [[UINavigationController alloc] init];
+	[nav setViewControllers:@[viewController, viewController2]];
+	NSString* title = @"Title";
+
+	[nav rnn_setBackButtonIcon:nil withColor:nil title:title];
+	XCTAssertEqual(title, viewController.navigationItem.backBarButtonItem.title);
+}
+
+
+@end

lib/ios/UINavigationController+RNNOptions.m

 	UIViewController *lastViewControllerInStack = self.viewControllers.count > 1 ? [self.viewControllers objectAtIndex:self.viewControllers.count-2] : self.topViewController;
 	
 	backItem.title = title ? title : lastViewControllerInStack.navigationItem.title;
+	backItem.tintColor = color;
 	
 	lastViewControllerInStack.navigationItem.backBarButtonItem = backItem;
 }