Lefty...I have the same unit but haven't been able to get out for last 3 weekends :^( so I don't recall exactly how the display looks but the menus are designed to be clear to read (thus solid) so I don't think there is a menu transparency setting. I will check the owners manual and see if there is anything obvious.
I love mine and will be upgrading the Navionics chip to 2010 next year so I can get more HD contours on more lakes.
Mike - I looked the manual over several times, no hint of whether or not you can adjust this. I saw the transparency option on Big John's Lowrance 520 unit, and kind of assumed that, since the HD5 is a new model, they would have included this feature. Guess I could fire an email to their support. Other than that, I really like the unit. If you haven't done it already, be sure to update the Lowrance firmware on their site to version 3.0 - doing this gives you more contour lines and detail, even when using the Navionics chip.