To change the lightbox background, you can use custom css. Please add the css to the ignite gallery options:
Please add css like this:
You can edit the color values in the css. 255,255,255 is a rgb color value, this sets the color of the lightbox background.
0.8 is the transparency of the background, it can be set from 0.0 to 1.0.
#999999 sets the the lightbox text, it can be any hexadecimal color.
If you need assistance with css changes, please contact ignite gallery support.