Hi Shell,
Sorry about your bad coloring experience. As people have already stated, henna or hennalucent is not a good choice when wanting to lighten your hair.
Hennalucent, like a lot of hair colorants, have images on packages or on the internet that are not truly representative of the color that you will achieve. This is for a number of reasons that include the printer who makes the label is only working on a representation of the color and then creates another representation of the color. Don't look for true color on packaging. Some brands do better than others but none can promise you the color on the package. On websites, the color you see has a lot to do with your monitor settings and regardless of the actual color of the image, you can see something different from your monitor.
The other reason the colored images of hair on packaging and websites can never promise you that what you get will be the same has to do with the individual nature of you own hair. A single color powder made into paste and put on two different people's hair for the same length of time can produce two different colors. Even if the two people appear to have the same color hair, one person's hair can take the color better than the other and get deeply intense color while the other person's hair resists color and they will get far less coloring. One person's hair may pick up in any red that is in the color and another person's hair might not. So one person might need to put the paste on their hair and time for 15 minutes and then rinse out...while another might have to leave it on for 6 to 8 hours to get the same intense coloring. The easiest way to predict you color results, even with Hennalucent, is to perform the harvest hair test that I suggest for 100% natural henna or herbal/henna for hair coloring. Test out the time/color connection for your hair. It will vary from person to person.
That said, however, you can allow the black coloring to fade over time...Or...know that you can shift the color. Using a henna powder or Hennalucent or herbal/henna that is "Natural" will begin to shift the coloring back to reddish/brown. It will provide reddish highlights and gradually shift the color back. It should definitely take the harshness from the black. Someone more familiar with the Hennalucent color chart than I can tell you what colors lean towards producing the reds. Those are the colors that will take the edge off the black and produce the highlights.
Try to avoid using anything harsh on your hair to shift the coloring. Getting from black to a more reddish/brown and then brown is not a hard stretch. Using the natural shade on black hair inevitably shifts the black. It can't lighten the hair to a light brown...but dark brown is within its range.
You can control the outcome often by doing the harvested hair test on hair from your comb and tweaking your process based upon what you observe.
Hope this helps.
HennaJoy