【编辑工具】添加背景模版，勾选File不应携带Color属性

PDF Office/PDF Master/Class/PDFTools/Background/New/View/KMAddBackgroundView.swift

@@ -357,7 +357,7 @@ class KMAddBackgroundView: KMBaseXibView, NSComboBoxDelegate {
             browseButton.isEnabled = true
             ratioTextField.isEnabled = true
             ratioStepper.isEnabled = true
-            background.color = nil
+            background.color = NSColor.white
             background.type = .file
             background.scale = ratioStepper.doubleValue
             doneButton.isEnabled = filePathLabel.stringValue.count > 0