make farmland paler

Continuation of #338 and #599. It slighly improves #102.

Farmland is still too aggressive and I think that making it a bit paler would be a good idea.

![selection_006](https://cloud.githubusercontent.com/assets/899988/4474992/63cd6fe6-4967-11e4-90d7-2371f20bcea4.png)
![selection_007](https://cloud.githubusercontent.com/assets/899988/4474993/68cb211e-4967-11e4-9d1c-91e0fce6c930.png)
![selection_008](https://cloud.githubusercontent.com/assets/899988/4474995/6a7c6658-4967-11e4-9101-a8d91d550cd9.png)