I can't imagine not having color -- for legibility and the ability to interpret the display quickly.

We are big fans of the Ray ecosystem. That said, we had a similar issue with one unit on a power boat. We have a Ray unit that we love (maybe the third we've owned), but added a smaller unit in the same series that was harder to see in sunlight. It turned out that the small units simply didn't turn out the same display brightness.

You want to look for the number of NITS (or 'nits') -- it's a measure of display brightness that should be listed somewhere in the specs. (I've noticed that laptop and tablet makers seem to be advertising this info more.) We saw the new Ray eS displays (different from the e series) and they are noticeably brighter, with a higher NITS spec. Nice units -- you might check them out.