The user who asked how to highlight a single gridline in a line chart is asking the wrong question. They are looking for a formatting trick inside a tool that was never designed to give them that control, and the real answer is that they should not have to fight the software to make their data speak clearly. This is not a criticism of the user, it is a critique of the tool.
When you need to call attention to a specific threshold, a target date, or a critical value, you should not be digging through obscure formatting menus or adding phantom data series just to make one line look different. Traditional spreadsheets treat every gridline as identical because they were built for static reporting, not for dynamic storytelling with data. The user in this case is trying to do something perfectly reasonable: mark a moment in time or a value boundary so that the audience instantly sees what matters. The fact that this requires a workaround tells you everything about the limitations of legacy spreadsheet software.
What this means in practical terms is that you are spending cognitive energy on the mechanics of presentation rather than on the substance of your analysis. Every minute you spend figuring out how to fake a colored gridline is a minute you are not spending interpreting what that line means for your business or your project. The tool should handle the formatting so you can focus on the insight. Modern AI-native spreadsheet technology does exactly that: it understands your intent. You say "highlight the line where sales crossed the target," and the chart updates. You do not need to know where the gridline settings live or whether you have to stack multiple series to create a visual effect. The software does the heavy lifting because it understands the context of your data, not just the coordinates of your cells.
The takeaway here is straightforward. If you are spending time on Reddit asking how to format a single gridline, you are working with the wrong tool. The problem is not your skill level, it is that the tool was designed for a world where data was static and charts were final outputs. We now live in a world where data changes constantly, and your charts should change with it. Stop asking how to hack a gridline. Start asking what your data is trying to tell you, and use a tool that lets you answer that question without a fight.