This is the FG/BG (Foreground/Background) icon just below the color picker and just above the Tool Options tab/dialog on my screenshot, the 2 colored squares.
The one on top/above is the FG, the one below/partly underneath is the BG.
click on that tiny angled double arrow to invert FG/BG before to pick the second color, the FG will become BG and vice-versa, like that you will have the 2 colors on the FG/BG icon. The tiny black and white squares just below is to reset to default B&W when clicking on it. Tip: You can click, stay clicked and drag n drop a color from the FG or BG directly on a layer to fill a layer or selection on the canvas.
Or use the Color picker tool to set FG or BG color in its Tool Options ➤ https://docs.gimp.org/2.10/en/gimp-tool-...7473653600 (the link is direct to the paragraph you need for fast reading )
The one on top/above is the FG, the one below/partly underneath is the BG.
click on that tiny angled double arrow to invert FG/BG before to pick the second color, the FG will become BG and vice-versa, like that you will have the 2 colors on the FG/BG icon. The tiny black and white squares just below is to reset to default B&W when clicking on it. Tip: You can click, stay clicked and drag n drop a color from the FG or BG directly on a layer to fill a layer or selection on the canvas.
Or use the Color picker tool to set FG or BG color in its Tool Options ➤ https://docs.gimp.org/2.10/en/gimp-tool-...7473653600 (the link is direct to the paragraph you need for fast reading )