A quick tip that I have to look up every time I use it. To generate nice random colors, use the HSV representation. Take random values for hue, and fixed numbers for saturation and value. This gives colors that work together, without looking too random.
srand48(time(0)); [[UIColor colorWithHue:drand48() saturation:0.5 brightness:0.95 alpha:0.5] setFill];