What are the most effective methods for painting intricate designs or patterns on a bike frame, considering factors such as durability, color retention, and the potential for damage from road debris or mechanical stress? Specifically, how do airbrushing, stenciling, and freehand techniques compare in terms of their ability to produce high-quality, long-lasting designs, and what types of paint and surface preparation are required for each method? Are there any advantages to using a single-color design versus a multi-color design, and how do the different techniques impact the overall weight and aerodynamics of the bike? Can a DIY approach using specialized bike paint and a well-ventilated workspace produce results comparable to those achieved by a professional bike painter, and what safety precautions should be taken when working with paint and chemicals?