Why the line 9999 in S125 becomes yellow?

[TurboTax-Duncan]

Hi, thank you for using Intuit TurboTax Community

Move your cursor over the line 9999 entry field to see the warning over that field. Usually there is a warning on s125 if entries are not made for income and expenses. If this is a NIL return and it is correct that s125 has no entries, signoff the warning.

Hope this helps