Her Red Lantern costume with it's red (well, duh) and black fitted very well with her frustration and anger at the moment she got the ring. It gives a nice visual cue to her inner workings and the tone of her adventures of that moment and when she overcame her darker impulses, she switched to happier colours. A rather hefty amount of symbolism that cannot be easily ignored. Life is filled with ups and downs and comics as a very visual medium has the opportunity to show it through more than just words.