Some people just put masking tapes around the bottom of the outside.
Some put scenic pictures around the base.
You could also paint the outside, i guess.
I've never had a problem with the glass walls, but if I did, I would just cut a strip of some sort of paper and tape it around the bottom edge, on the outside of the glass.
When a turtle or tortoise has problem with glass it's usually to the point that the enclosure is to small. However, You can put anything on the outside to cover it. Most pets stores even sell the decorative stickers