made internal since there is a duplicate in coreUI that is obj-c

Signed-off-by: Matt Bruce <matt.bruce@verizon.com>

VDS/Extensions/UIColor.swift

@@ -193,7 +193,7 @@ extension UIColor {
         self.init(red: CGFloat(r) / 255, green: CGFloat(g) / 255, blue: CGFloat(b) / 255, alpha: CGFloat(a) / 255)
     }
     
-    public func isDark() -> Bool {
+    internal func isDark() -> Bool {
         var white: CGFloat = 0
         var alpha: CGFloat = 0
         if getWhite(&white, alpha: &alpha) {