Here's what's happening: you built a working hours chart with formulas that return a blank string, `""`, for cells that have no data yet, and then you told Excel's conditional formatting to color every cell above zero green. The problem is that Excel reads an empty string as text, and when it compares text to a number, it treats the text as larger than zero. So all your blank overtime cells light up green, pretending they contain a positive value. That's not a bug in your logic; it's a gap in how conditional formatting evaluates empty results.
The practical fix is straightforward: make your formula produce a true blank rather than a text string. In Excel, the functions `ISBLANK` and a conditional format rule that explicitly checks for blank cells can solve this, but the cleaner approach is to leave the cell actually empty when there's no input. Instead of `""` in your IF statements, use an empty pair of quotation marks with no space, that still returns a blank string. But for conditional formatting to ignore those cells, you need a rule that says "stop if cell is blank." Alternatively, change the formula to return zero as a number and then adjust your formatting rule to color only values strictly greater than zero, because zero is not greater than zero, and blank cells that return zero stay clear. A third option: use `ISNUMBER` in your conditional format rule so that only numeric values trigger the color.
What this tells us is that spreadsheets, even familiar ones like Excel, have subtle assumptions about data types that catch people constantly. The user here did everything right by Googling and building formulas step by step, but the tool itself made a silent choice, treating a text string as larger than a number, that broke a simple visual check. That's not a user error; it's a design limitation that forces people to learn edge cases instead of focusing on their actual task, which is tracking hours.
The takeaway is clear: if you're building a spreadsheet that relies on conditional formatting, always test how your formulas behave when inputs are missing. Use `ISBLANK` as a guard, return zero instead of an empty string when you mean "no value," or apply a separate formatting rule to skip blanks entirely. One extra rule now saves you from staring at a green column full of nothing, wondering why the tool didn't see what you saw. That's the difference between a spreadsheet that works for you and one that works in theory.