What is the color of the sky?
The sky is gray.
    src        edge_attr  dst
0     0               by    6
1     2               by    4
2     2               by    6
3     2               in    8
4     3               of    2
5     3   to the left of   16
6     6               by    2
7     7               of    2
8     8               by    2
9     9               by    6
10   10               by    6
11   13               by    2
12   14               by    2
13   15   to the left of   16
14   15               of    2
15   16  to the right of   15
16   16  to the right of    3
17   16               of    2
18   17               of    2