There is a single large rock model with what appears to have a bugged texture. Instead of the regular stone texture, it is a single, solid color, that seems to vary depending on the time of day - sometimes it's blue on clear days, and other times it shifts between multiple shades of blue and purple.

It has only appeared in the .62 experimental branch, and I have seen it on multiple exp servers over the course of the last few patches of .62.

It is located near Stary Yar, only 2 meters south of the wrecked police car spawn point on the eastern edge of town.

Here is a screenshot (imgur link).