I am making the hat in the noob to pro tutorial. I now need to select all the bottom vertices of the hat. Two of the vertices do no become “Completely” yellow when I try to select them. Therefore I am unable to select the bottom of the hat as a region and I cannot extrude. I would include a pic but it wouldn’t help.
They all look the same. 
Try hitting Z to goto Wireframe before selecting.
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