You could select all the cells in the area you are using, or select the entire worksheet. You can do that by pressing Ctrl-A or clicking the Select All button, which is the blank one above the row 1 header and the beside the header for column A. Then press Ctrl-1 to go to Format Cells and go to Patterns and you can pick a colour. It will be applied to the area selected.
Right-click on the tab and select option for tab color.
Fill Color
blue
Yes it is.
The color of the text gets bold and black on the active sheet tab against a white background. You also have the option to change color of your choice.
Yes it does. You have to do a right click on the tab and select tab color and then select the color you want !
When you change the color of the fill in a cell you are changing its format. This action applies to Microsoft Excel.
If this feature has been protected then you must "unprotect" the worksheet first. If you do not have the password to do this then I'm afraid you are using a spreadsheet in which the creator did not want you to change such things (and they probably had a good reason to do so).
color coding
go to layout, then click on color (it has a picture of a paint bucket) and click on a color to change your background
Rename the tabs for each worksheet to identify the data they contain, Insert a new worksheet after the first worksheet, change the color of the tabs related to each project
shading