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.

How to Change the Color Coding on a Microsoft Excel Graph Legend. Color can make it easier for people to identify important information, such as legends on an Excel graph. Professional designers ...

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.