I would color this coloring page with bright, vibrant colors. For Baymax, I would use reds and whites to illustrate the curve of his fist and to make his cape pop. His eyes could be a dark yellow to represent determination, while the cityscape in the background could be filled in with various blues and greens to bring a feeling of life and excitement. The overall picture could be made to look unified using a warm glow of oranges, pinks, and reds.