Sure! I couldn't figure out how to attact an example to the palette but my icon image is what I used it for

I think you could get away with brightening the black to match the palette's other lighter colors. That color could range anywhere from a smidge above true black or something more akin to Clément 8's navy "black". (But I'm not recommending you steal that palette's exact color)

As for the palette example: read the rules on the bottom of the example submission page first, make sure your final submission is exactly 464x120 pixels (you can scale a smaller canvas up to get there), and put in your best effort into making the example image. The last is most helpful for getting your palette approved. If you still have any difficulties with submitting an example ask the discord linked at the bottom of this page. It is the middle icon under "Follow Lospec."