I am trying to change the color of a cell that equals other multiple cells.
I’m afraid that questions related Excel (specifically, Excel 2010, according to tags) should be asked at Microsoft site.
Of course, Libreoffice Calc is the better solution and can easily put into effect what the questioner wants to achieve by conditional formatting. Fill in one CF dialogue for 30. Done!
I’m assuming that you want to know how to do this in Calc.
Left click cell M3. Select Format → Conditional Formatting → Condition…
Change “Cell value is” to “Formula is”. Enter “IF(COUNTIF(A1:L20,M3)>0)” as the function. Click “Accent” to the right of “Apply Style:”. Click “New Style…”. Click “Background”. Select your desired color. Click “Okay” or hit enter.
COUNTIF(A1:L20,M3) → This adds a running sum of +1 for each match of the string in M3 to every cell from A1 to L20. If there is at least one match, then the result returned will be more than 0.
If you wanted excel, then it would be similar. Try following Microsoft’s instructions for conditional formatting.
More information related to this for Calc/LibreOffice.
https://help.libreoffice.org/Calc/Applying_Conditional_Formatting
https://help.libreoffice.org/Calc/COUNTIFS_function