Help getting background invisible so background image shows thru!

Can I get some advice? I need to make the background color of my "Body line background" into "nothing" or "invisible" (right now it is grey -- #9E9E9E, but won't allow me to delete it to nothing) so that I can see the background image I've placed behind it through it. Does that make sense?

Background image is a grey parchment thing.

URL is: https://i.servimg.com/u/f84/14/24/53/91/i_back10.jpg

And my site is: http://requiemnc.forumotion.com/index.htm

You can see the grey parchment peeking through on the sides -- just can't figure out how to get the main background to go invisible so I can see the whole thing.

Thanks for the help!



Oh -- this is the skin information:

Vista Grey

Created on 2008-08-02 by Van1lla

Version :
Phpbb 3

Personal Css :
Yes

Category :
Various...

Description :
This is my very first theme.Im Anime from forumotion.

Do you want your given image to be transparent? if so how much precent?

that's not necessary. the image is at the very back so it can be solid. but it could be ok to go 10% lighter or so if necessary...

??