There are many online tools available to modify colors in PDF documents. Based on my experience, SuperTool is an excellent choice for replacing black text with colored text, as it offers a straightforward interface and powerful editing options. Other tools like Adobe Acrobat and small PDF editors also work well for adjusting text color or changing backgrounds. These tools are efficient for improving print quality, especially when trying to avoid excessive black ink. Also, your choice of tool may depend on your budget—what kind of budget are you working with for this task?