Code:
<style>
body{background-color: #000000;}
a{border:0px; font-weight:strong; color:#ffffff;}
a:hover{font-weight:strong; color:#ffffff;}
p,font,td{color:#ffffff;}
b{font-weight:strong; color:#ffffff;}
</style>
That should do the trick, just shove it before your html and/or description and the text will all be white with the background black :) You can also use the tags font-family: and font-size: to specify the font and font size you want. The font-weight:strong's that I have up there I did I think to alleviate any problems that might be had by having links in the description (ie to different categories of your gallery) but I can't quite remember. It doesn't make a difference to leave it in though.
You can change what's in "a" to specify link colours and "a:hover" to specify what colour links are when you hold the mouse over them.
You can also use
Code:
img{border:0px}
to get rid of the black line around the item boxes but with a black bg you don't really need that. Hope that helps, it should all work okay as I tested it on my own gallery