Fix grass main colors

[ChillerDragon]

Closes #61

before

$ grep 325021 mapres/grass_main.svg  | wc -l
2

$ grep 324f21 mapres/grass_main.svg | wc -l
14

$ grep 9ee741 mapres/grass_main.svg | wc -l
2

$ grep 9fe743 mapres/grass_main.svg | wc -l
14

after

$ grep 325021 mapres/grass_main.svg  | wc -l
0

$ grep 324f21 mapres/grass_main.svg | wc -l
16

$ grep 9ee741 mapres/grass_main.svg | wc -l
0

$ grep 9fe743 mapres/grass_main.svg | wc -l
16