Fill with BG Color

`Ctrl` + `.`

All hotkeys for GIMP (Windows)

Edit Shortcuts Undo	`Ctrl` + `Z`
Edit Shortcuts Redo	`Ctrl` + `Y`
Edit Shortcuts Cut	`Ctrl` + `X`
Edit Shortcuts Copy	`Ctrl` + `C`
Edit Shortcuts Copy Visible	`Shift` + `Ctrl` + `C`
Edit Shortcuts Paste	`Ctrl` + `V`
Edit Shortcuts Past as New Image	`Shift` + `Ctrl` + `V`
Edit Shortcuts Clear	`Delete`
Edit Shortcuts Fill with FG Color	`Ctrl` + `,`
Edit Shortcuts Fill with BG Color	`Ctrl` + `.`
Edit Shortcuts Fill with Pattern	`Ctrl` + `;`
View Shortcuts Shrink Wrap - Reduce image window to size of image	`Ctrl` + `E`
View Shortcuts Toggle Fullscreen View	`F11`
View Shortcuts Show Selection	`Ctrl` + `T`
View Shortcuts Show Guides	`Shift` + `Ctrl` + `T`
View Shortcuts Show Rulers	`Shift` + `Ctrl` + `R`
File operations New Image	`Ctrl` + `N`
File operations Create a new Image from Clipboard	`Shift` + `Ctrl` + `V`
File operations Open Image	`Ctrl` + `O`
File operations Open as Layers	`Ctrl` + `Alt` + `O`
File operations Save Image	`Ctrl` + `S`
File operations Save As	`Shift` + `Ctrl` + `S`
File operations Print	`Ctrl` + `P`
File operations Close	`Ctrl` + `W`
File operations Close All	`Shift` + `Ctrl` + `W`
File operations Quit	`Ctrl` + `Q`
Layer Shortcuts New Layer	`Shift` + `Ctrl` + `N`
Layer Shortcuts Duplicate Layer	`Shift` + `Ctrl` + `D`
Layer Shortcuts Anchor Layer	`Ctrl` + `H`
Layer Shortcuts Select Previous/Next Layer	`Page Up` / `Page Down`
Layer Shortcuts Select Top/Bottom Layer	`Home` / `End`
Select Shortcuts Select All	`Ctrl` + `A`
Select Shortcuts Select None	`Shift` + `Ctrl` + `A`
Select Shortcuts Invert Selection	`Ctrl` + `I`
Select Shortcuts Create a Floating Selection	`Shift` + `Ctrl` + `L`
Select Shortcuts Select by Color	`Shift` + `O`
Select Shortcuts Select from Path	`Shift` + `V`
Select Shortcuts Toggle Quick Mask	`Shift` + `Q`
Image Operations Duplicate Image	`Ctrl` + `D`
Image Operations Merge Visible Layers	`Ctrl` + `M`
Image Operations Display Image Properties	`Alt` + `Return`
Selection Tools Rectangle Select	`R`
Selection Tools Ellipse Select	`E`
Selection Tools Free Select	`F`
Selection Tools Fuzzy Select	`U`
Selection Tools Select by Color	`Shift` + `O`
Selection Tools Intelligent Scissors	`I`
Paint Tools Bucket Fill	`Shift` + `B`
Paint Tools Blend	`L`
Paint Tools Pencil	`N`
Paint Tools Paintbrush	`P`
Paint Tools Eraser	`Shift` + `E`
Paint Tools Airbrush	`A`
Paint Tools Ink	`K`
Paint Tools Clone	`C`
Paint Tools Heal	`H`
Paint Tools Blur / Sharpen	`Shift` + `U`
Paint Tools Smudge	`S`
Paint Tools Dodge / Burn	`Shift` + `D`
Transfrom Tools Align	`Q`
Transfrom Tools Move	`M`
Transfrom Tools Crop	`Shift` + `C`
Transfrom Tools Rotate	`Shift` + `R`
Transfrom Tools Scale	`Shift` + `T`
Transfrom Tools Shear	`Shift` + `S`
Transfrom Tools Perspective	`Shift` + `P`
Transfrom Tools Flip	`Shift` + `F`
General Paths	`B`
General Color Picker	`O`
General Zoom	`Z`
General Measure	`Shift` + `M`
General Text	`T`
General Toolbox	`Ctrl` + `B`
General Default Colors (Sets foreground to black and background to white)	`D`
General Swap Colors	`X`
Dockable Dialogs Layers	`Ctrl` + `L`
Dockable Dialogs Brushes	`Shift` + `Ctrl` + `B`
Dockable Dialogs Patterns	`Shift` + `Ctrl` + `P`
Dockable Dialogs Gradients	`Ctrl` + `G`
Dockable Dialogs Toolbox	`Ctrl` + `B`
Help Menu Help	`F1`
Help Menu Context Sensitive Help	`Shift` + `F1`
PlugIn Shortcuts Repeat Last PlgIn	`Ctrl` + `F`
PlugIn Shortcuts Plug In	`Shift` + `Ctrl` + `F`
Selection Shortcuts Select All	`Ctrl` + `A`
Selection Shortcuts Select None	`Ctrl` + `Shift` + `A`
Selection Shortcuts Invert Selection	`Ctrl` + `I`
Selection Shortcuts Toggle Selection	`Ctrl` + `T`
Selection Shortcuts Path to selection	`Shift` + `V`
Selection Shortcuts Float Selection	`Ctrl` + `Shift` + `L`