Add an optional delegate method to change the color of dimming background overlay

Source/JTSImageViewController.h

@@ -154,6 +154,10 @@ extern CGFloat const JTSImageViewController_DefaultBackgroundBlurRadius;
  Defaults to `JTSImageViewController_DefaultAlphaForBackgroundDimmingOverlay`.
  */
 - (CGFloat)alphaForBackgroundDimmingOverlayInImageViewer:(JTSImageViewController *)imageViewer;
+/**
+ The default color is `[UIColor blackColor]`.
+ */
+- (UIColor *)colorForBackgroundDimmingOverlayInImageViewer:(JTSImageViewController *)imageViewer;
 
 /**
  Used with a JTSImageViewControllerBackgroundStyle_ScaledDimmedBlurred background style.

Source/JTSImageViewController.m

@@ -427,7 +427,7 @@ - (void)viewDidLoadForImageMode {
     self.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
 
     self.blackBackdrop = [[UIView alloc] initWithFrame:CGRectInset(self.view.bounds, -512, -512)];
-    self.blackBackdrop.backgroundColor = [UIColor blackColor];
+    self.blackBackdrop.backgroundColor = self.colorForBackgroundDimmingOverlay;
     self.blackBackdrop.alpha = 0;
     [self.view addSubview:self.blackBackdrop];
 
@@ -496,7 +496,7 @@ - (void)viewDidLoadForAltTextMode {
     self.view.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
 
     self.blackBackdrop = [[UIView alloc] initWithFrame:CGRectInset(self.view.bounds, -512, -512)];
-    self.blackBackdrop.backgroundColor = [UIColor blackColor];
+    self.blackBackdrop.backgroundColor = self.colorForBackgroundDimmingOverlay;
     self.blackBackdrop.alpha = 0;
     [self.view addSubview:self.blackBackdrop];
 
@@ -996,6 +996,19 @@ - (UIColor *)backgroundColorForImageView {
     return backgroundColor;
 }
 
+- (UIColor *)colorForBackgroundDimmingOverlay {
+
+    UIColor *color;
+
+    if ([self.optionsDelegate respondsToSelector:@selector(colorForBackgroundDimmingOverlayInImageViewer:)]) {
+        color = [self.optionsDelegate colorForBackgroundDimmingOverlayInImageViewer:self];
+    } else {
+        color = [UIColor blackColor];
+    }
+
+    return color;
+}
+
 #pragma mark - Dismissal
 
 - (void)dismissByCollapsingImageBackToOriginalPosition {