Some normals won't point outward . . . WHY?

I made a Helicopter model today and when I went to render it, preview render, with shift-P in object mode it showed a black area on what was supposed to be a blue tail fin. I tried recalculating normals out side but nothing happened. This has happened before and now I want to ask for some help in solving this annoyance. Does anyone know how get rid of the black spots.

I have tried selecting the faces and shifting the normals individually before and it doesn’t do anything either.

So, if you have a fix please let me know . . . and if you could explain why this happens that would be cool, too. Actually, I kind of know how it happens but still . . . I can’t figure out how to fix it.

Let me know if this is just me or if it happens to everyone sometimes . . .

A couple possible reasons.
most likely, the mesh is open somewhere (as in, not closed) or is non-manifold, so “outside” is not well defined in terms of the mesh.

You can try selecting the offending faces and flipping their normals manually (flip normals in the edit buttons window)
[Edit: I see you’ve tried this already]

also, you may have doubled faces or vertices. Try rem-doubles (also in edit buttons) before recalculating normals.

If nothing seems to work, last ditch would be to delete the offending region and recreate it/reface it manually.
Activate draw normals in edit buttons to help with manually flipping normals, or deleting and recreating errant faces.

I’ve noticed sometimes the render preview doesn’t update unless you do a full on render. Everybody has problems with normals, many have problems with recalculate normals either doing nothing because the mesh is “calculated” correctly according to its algorithm, or switching some faces back and forth, again, because it can’t figure out the mesh. zdk1 outlined a lot of the common reasons it happens, but to get more specific we’d need to see a screenshot or two. Sometimes when creating thin rectangular prisms, you can get it turned inside out, and you are actually seeing the inside of the tail fin exposed to the outside (if that makes any sense) and the blue color is exposed on the inside.

In edit mode, select the region with the problem, click mesh>normals>recalculate outside (Ctrl+N). Not sure if that helps, but it’s worth trying.