The odor is a good question! As to the dark color, is it tea-colored? that could happen if some leaves or other organic matter found it's way into the container. By itself, that tea/tannin color should not be a problem. That color could happen if the water is collected and stored rain water.
If there is a questionable odor, or there are other doubts, siphon it out, and start over. Water isn't free, but it is relatively inexpensive, in relation to taking a risk with plants that are more of an investment.
