Which color is the skateboard the boy is riding on?
The skateboard is gray.
    src        edge_attr  dst
0     0          wearing    4
1     0        riding on    3
2     0             near    1
3     0               on    3
4     0             near    2
5     0  to the right of    6
6     0             near    6
7     1             near    5
8     1             near    2
9     1             near    0
10    1  to the right of    5
11    2            below    3
12    2             near    1
13    2             near    0
14    5             near    1
15    5   to the left of    1
16    6   to the left of    0
17    6             near    0