diff --git a/README.md b/README.md
index eca7824..1ebfc01 100644
--- a/README.md
+++ b/README.md
@@ -64,6 +64,8 @@ Add your issue here on GitHub. Feel free to get in touch if you have any questio
 
 (There are no corresponding tags in the project. I only keep such a history in this README.)
 
+- v0.15 (2018-05-02)
+  - `Flex` and `Grid` don't clear their background per default, thus allowing for custom modals. See the [Wiki](https://github.com/rivo/tview/wiki/Modal) for an example.
 - v0.14 (2018-04-13)
   - Added an `Escape()` function which keep strings like color or region tags from being recognized as such.
   - Added `ANSIIWriter()` and `TranslateANSII()` which convert ANSII escape sequences to `tview` color tags.
diff --git a/box.go b/box.go
index a552c3d..086ff5a 100644
--- a/box.go
+++ b/box.go
@@ -223,9 +223,11 @@ func (b *Box) Draw(screen tcell.Screen) {
 
 	// Fill background.
 	background := def.Background(b.backgroundColor)
-	for y := b.y; y < b.y+b.height; y++ {
-		for x := b.x; x < b.x+b.width; x++ {
-			screen.SetContent(x, y, ' ', nil, background)
+	if b.backgroundColor != tcell.ColorDefault {
+		for y := b.y; y < b.y+b.height; y++ {
+			for x := b.x; x < b.x+b.width; x++ {
+				screen.SetContent(x, y, ' ', nil, background)
+			}
 		}
 	}
 
diff --git a/demos/modal/centered.png b/demos/modal/centered.png
new file mode 100644
index 0000000..7511a05
Binary files /dev/null and b/demos/modal/centered.png differ
diff --git a/flex.go b/flex.go
index 5648b4a..4a7b419 100644
--- a/flex.go
+++ b/flex.go
@@ -33,17 +33,24 @@ type Flex struct {
 	// FlexRow or FlexColumn.
 	direction int
 
-	// If set to true, will use the entire screen as its available space instead
-	// its box dimensions.
+	// If set to true, Flex will use the entire screen as its available space
+	// instead its box dimensions.
 	fullScreen bool
 }
 
 // NewFlex returns a new flexbox layout container with no primitives and its
 // direction set to FlexColumn. To add primitives to this layout, see AddItem().
 // To change the direction, see SetDirection().
+//
+// Note that Box, the superclass of Flex, will have its background color set to
+// transparent so that any nil flex items will leave their background unchanged.
+// To clear a Flex's background before any items are drawn, set it to the
+// desired color:
+//
+//   flex.SetBackgroundColor(tview.Styles.PrimitiveBackgroundColor)
 func NewFlex() *Flex {
 	f := &Flex{
-		Box:       NewBox(),
+		Box:       NewBox().SetBackgroundColor(tcell.ColorDefault),
 		direction: FlexColumn,
 	}
 	f.focus = f
@@ -96,8 +103,6 @@ func (f *Flex) RemoveItem(p Primitive) *Flex {
 
 // Draw draws this primitive onto the screen.
 func (f *Flex) Draw(screen tcell.Screen) {
-	f.Box.Draw(screen)
-
 	// Calculate size and position of the items.
 
 	// Do we use the entire screen?
diff --git a/grid.go b/grid.go
index 2088647..f7d61a5 100644
--- a/grid.go
+++ b/grid.go
@@ -59,9 +59,16 @@ type Grid struct {
 }
 
 // NewGrid returns a new grid-based layout container with no initial primitives.
+//
+// Note that Box, the superclass of Grid, will have its background color set to
+// transparent so that any grid areas not covered by any primitives will leave
+// their background unchanged. To clear a Grid's background before any items are
+// drawn, set it to the desired color:
+//
+//   grid.SetBackgroundColor(tview.Styles.PrimitiveBackgroundColor)
 func NewGrid() *Grid {
 	g := &Grid{
-		Box:          NewBox(),
+		Box:          NewBox().SetBackgroundColor(tcell.ColorDefault),
 		bordersColor: Styles.GraphicsColor,
 	}
 	g.focus = g