Are there any flags that are not yellow?
Yes, there is a blue flag.
    src        edge_attr  dst
0     1               on    7
1     1  to the right of   14
2     1   to the left of   10
3     5   to the left of   10
4     5   to the left of    7
5     7  to the right of   14
6     7  to the right of    5
7    10  to the right of    5
8    10  to the right of    1
9    12               on   10
10   14   to the left of    1
11   14   to the left of    7
12   15               on    0