Is it possible that your brightness setting is down? If not, one solution would be to tint your car - I had problems w/ my old headunit not being visible (alpine cd player), and my car gets pretty hot during the day anyways (I live in Florida..) so I opted to tint my car.. Makes the empeg quite visible during bright days...
-mark

MK2: 36gb
Tivo 90gb
Computer: 120gb disk space
...I think drive manufactureres love me!