More satured grass colour for Floating Mini Flower Islands

I find the "Alpha" type grass on the floating islands not really fitting
if I am, for example, in a forest biome. Thus, I satured the green in
the island to be a bit more dark and the result is quite pleasant :
http://imgur.com/hHskdCm

Thanks for reading

Yulife
Merge pull request #399 from Yulife/master

More satured grass colour for Floating Mini Flower Islands