Which of the following is a sign that air hoses may need replacing?

Bulging or swelling of air hoses is a significant sign that they may need replacing. This condition often indicates that there is a buildup of pressure or internal damage within the hose that could lead to a failure. Air hoses are designed to withstand certain pressures, and any deformation suggests that the structural integrity is compromised. These bulges can create weak spots that might rupture, leading to air leaks, which can severely impact brake performance and safety.

The other factors listed do not necessarily indicate a need for replacement. For instance, simply having a long or excessive length of hose isn't inherently problematic unless it exceeds specifications that could affect system performance or safety. Unusual coloring might suggest surface damage or exposure to chemicals but does not directly signify that a hose needs to be replaced, as it could also be a cosmetic change without impacting function. Hence, recognizing bulging or swelling as a clear warning sign is essential for maintaining the air brake system's safety and efficiency.