It Turns Grey

Why dose this happen??? I’ve asked this question before but only now I have a pic.

in edit mode, with all the faces selected: CTRL + N in order to recalculate the normals. it should solve your case.

anyway, when you have faces like this, you don’t need to smooth them: in the Editing buttons (F9 key), I suggest you to press the Set Solid button instead of the Set Smooth button…

hope this helps,