Having this problem with multiple meshes (so it's probably something easy I'm missing). I have these flat meshes I'm attempting to make into closed 3D objects. But the original vertex shapes become reflective and change colour when adding in a new face.
I'll select the vertexes for the edge of the face (pic 1) create a new face with F key (pic 2). But then BAM, all the faces that connected to those original vertexes have lost their colour and become shiny/reflective (pic 3). (You can also see the colour change from pic 1 to 2)
I'm wondering if there is a fix for this, or if I'm doing something wrong. Cheers in advance.