My interpretation is that you’re making a vanilla infusion – not an extract. You’ve no doubt seen flavoured vodkas – in which, e.g., the peel of fruit has been steeped in neutral vodka for some time. Herb vodkas and spiced vodkas (including a pepper vodka flavoured with either chillies or peppercorns) are also marketed.
Commercial vanilla extract is made by means of a recirculated percolation process. Each batch must be tested assiduously and standardized since all vanilla beans are not alike in flavour. Nevertheless, in order to make a successful batch of “vanilla essence” at home, the most assured result will probably derive from this procedure:
Split the vanilla beans lengthwise (say, 4 or 5 good-quality pods) and insert them into a bottle of unflavoured Vodka (for the sake of your wallet, don’t use a premium brand such as Grey Goose!). Recap the bottle, and allow it to sit at room temperature (in direct sunlight, when possible) for at least 3, perhaps as long as 5 weeks. Shake the bottle fairly vigorously every few days.
When the Vodka has acquired a deep amber colour, strain it through a double thickness of cotton muslin or cheesecloth into a bowl.
In a saucepan, make a simple syrup. Allow the syrup to cool, then add the vanilla-flavoured Vodka. Pour this combined mixture into a sterilized glass bottle; cover with a screw cap, and allow it to stand at room temp. for about 1 month.
Culinary experts agree that REAL vanilla extract is worth the price you pay. The seemingly high cost is due to the fermentation & curing process. Still, if your are thoroughly satisfied with your maceration of a vanilla beans in Vodka (or even brandy), then you have good reason to continue the enterprise. You will be able to take justifiable pride in your uniquely created flavoring.
To address your question re color of the product: That is, of course, irrelevant to a determination of quality. Synthetic vanilla made from courmarin may be the same color as the pure extract. However, would you use a dark rum instead of vodka? Then you’d have your black “extract” for sure!
Finally, the dark bottles in which commercial vanilla is usually marketed, are actually not essential to its preservation. The glass itself is the important factor: Vanilla will keep indefinitely when stored in glass as long as it is not exposed to extreme cold or heat.