This is because they are colorful and easy to identify among everyone else's cables when tearing down after a show. This helps in settling arguments as to who's cables are who's. If you really love the sound, spend the extra dough on one in better shape or treat yourself to a new one with a warranty. More importantly, make sure the amp is safe. Even if you're poor, you still can't afford to skimp on strings.
New strings have better intonation and sound brighter.
The absolute cheapest way to change your tone is to experiment with different picks. At 25 cents a pop, comparison shopping has never been so inexpensive. You'd be surprised at what a difference they make, especially on acoustic guitar. Also seek out picks that don't slip out of your hand. If you're on a budget, pedals seem to be the way to go.