All fresh brake fluid, right out of the bottle is just half a shade darker than water. Pouring it out it would appear clear, but if you look through a glass of it it would have a yellow or pinkish tint.
The fluid will yellow over time, then turn green, and eventually black. This happens as it absorbs water from the atmosphere. Bendix, the guys who make all the brake parts for everyone and are pretty much the top authority on brakes across the industry, recommends having the brake fluid changed out every 2 to 3 years.
Once it starts to turn colors like green or black it can, and probably will, discolor the plastic of the reservoir, so even if you drain everything completely and put fresh stuff in it still appears dark in the reservoir. I would get it changed out. At the very least doing the brake fluid regularly will keep the bleeder screws from seizing up, which means when you need a line replaced you won't have to replace a caliper or two as well just to bleed the brakes.