I have also bought the Garmin 176 C (color). It's a nice feature to have color's on all the markings out there. But as JWC says it's not an easy task to read the color display outside on the rib. I'm using the backlight all the time, and but the contrast up a bit. This seems to bee working. When I spoke to Garmin, they didn't tell me that this was going to be a problem, they told me that they had tried this many times before and only had problems when the sun was direct on the display (Bull sh..).
I would have return it, if it was not because I orderd mine from the US (I was less than half price), And yes I do have a road map of the US on this, but it dosn't matter, since I'm using the bluechart on it. (I might go to the US some times, and then I could use it for Road navigation)
I think you should have a look at the Garmin 182. I thing Grame has this one. It's the same setup but a bigger screen. And we all want bigger screens (Chart plotter, Computer monitor, Televison.....)