Macro for finding and changing cell colors

Hello,

I'm working on a large data file where on a monthly basis I have to check for any errors. I'm wanting to write a macro that allows for the following:

IF row G does not contain the value from E
OR row G does not contain the value from F
OR row G does not contain "[at]email.com"
Then change the cell color to purple

To clarify: E contains FirstName, F contains LastName, G contains emailadress with firstname.lastname[at]email.com. I'm looking for errors in the emailadress, where it may have been misspelled or the wrong format was used.

I'm not allowed to make permanent changes with formulas so cannot use vlookup/hlookup etc in the sheet itself, therefore I'm looking for a VBA code that will let me change the colors. I will then write an IF-ELSE, so I can undo my color-coding before saving the file.

What would be the best way to write this in VBA?

Thanks!