To change Gridline color in Excel, use Excel Options, apply a custom-colored border to the cells, or apply a custom line color. Full details here.

In case of an error, a triangle appears in the corner of the cell. You can change the Color of an Error Indicator from green to any other in Excel.

How to Make Colors Change With Validation in Excel. Excel's conditional formatting tool applies formatting depending on cells' contents. Validation rules can change cells font, style, size or border.

Click the "Color" drop-down menu to view a list of colors. Click one of those colors, and Excel applies it to the legend instantly.