I am in material preview mode and see the colors, but the loops (or any lines edges/faces) don't show.
I would upload a screenshot but don't see an option to upload...
maybe you have the overlay off. Press SHIFT + ALT + Z or go to the icon here. If it is blue, it is active and you should see Edges and Faces
An easy method to upload images here is also if you work with the Windows SnippingTool. You press WindowsKey+SHIFT+S then simply “frame” the area you want to screenshot and then just press CTRL+V in the text field at CGCookie to paste. At least that's how I do it.
Yes as Leo says, you may have Overlays turned off. For uploading the image, there is a hiccup on the website where if you are the first to post, the tools for uploading images and whatnot don't show up, so you have to upload your image on the second post or just edit the first one after you have posted. That error seems to have been for far too long and it hasn't been patch, so we just live with it until the time comes it gets corrected.
There's a known bug where you can't attach an image when you post under a video. You can do Leo's method or just do a reply to your initial post inwhich case you can then attach an image.
Henlow to anyone concerned! It seems like there is no color-code on the mug cup! Please see the overlay, material pane and the Material Preview!
(Unfortunately, I get Access Blocked when I try to upload a screenshot directly, so I have uploaded to Imgur.)
https://imgur.com/a/5wEEcVb
