Click a key to hear its pitch (A4 = 440 Hz). Pick a color, then click or drag across the grid to mark your range for each mode. Everything is saved in this browser automatically — use Download / Upload JSON to back it up or move it.
How to mark a range: click a cell to fill it with the current color, click it again to clear it. Press and drag to fill a whole stretch at once. Switch to Eraser and drag to wipe an area. Each cell can hold its own color, so you can use a darker green for your comfortable range and a lighter shade or yellow for the edges. Click a mode label (or the top-left corner) to collapse the list to numbers and see more of the keyboard.