Gridlines are useful in Excel helping to specify each cell, by default, it appears in light gray when you open a workbook. However, if you want to change them to a different color (e.g., red), please follow the steps below:
Step 1: Click the "File" Tab from the ribbon;
Step 2: Click "Options" from the left navigation menu;
Step 3: Click "Advanced" from the left navigation menu in the dialog box;
Step 4: Select a color from "Gridline color" (e.g., red) under the section of " Display options for this worksheet";
Step 5: Click "OK" at the bottom to apply the changes.