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When there are multiple cells in the list the selected cell is clearly highlighted indicated by a different frame and cell size to the rest of the cells.
Cell selection works by simply clicking on a cell. All the actions the colour list editor offers work on the selected cell including:
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These actions can be triggered either from the buttons
button at the top of the helper editor or from the context menus of the cells (right-click on a cell to get the context menu).
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