This subject is near and dear to my heart....
I have used three types of levels: Rail mount, scope mount, and internal (built into the scope). All have their good points, and bad points. Rail levels will always assure a level gun, but if the scope isn't mounted correctly, you'll still get cant! Scope mounted levels have the same issue, as do built in levels. One way around the issue is to use a rail mounted level, and a scope with a build in one. Once they're both mid level, your scope mounting should be dead on. But there are another issues, and ones often over-looked.
I have three scopes with built in levels. All three have the same issue when pointing eastward during the morning hours—sun glint off the level itself! A sun shade helps, but with one of the scopes (a Hammer's SF), the sun shade wasn't enough. I added a honeycomb sun shade on the front of the sun shade, and the problem (mostly) went away.
The other issue is simply the field of view. Although the amount of viewing area taken by the level (always mounted at the bottom of the scope) is small, the level's movement can be disconcerting when you're scanning the country side. You sort of get used to it, fortunately, but it has taught me to rely more on the binoculars which is a good thing.
Let me add this. The color is a personal choice, but I too like the green rather than the yellow. And you don't have to spend big bucks. The best rail mounts I have all cost less than $10 each on Amazon.
