In many technical diagrams, particularly in engineering and drafting, different colors can be used to represent various axes or dimensions. However, there isn't a universal standard for the color of arrows indicating the width of an object or the X axis, as it can vary by context.
That said, a common practice is to use:
- Red for the X-axis in some diagrams.
- Blue for the Y-axis.
- Green or other colors might be used for the Z-axis or additional dimensions.
In your list, the red arrow is often used to indicate the X-axis, so it would be a reasonable choice if you are following a convention that uses color coding.
If you have a specific context or example in mind, please provide more details!