Hello Umberto. What is wrong with the night textures for taxyways. Is this the way it is suppose to look? It looks like the taxyways are grass.
I don't see anything wrong your screenshot, or anything that resembles grass. It's just that FSX night blending with airplane lights, due to usage of DXT compression ( using 32 bit textures for ground will *destroy* the fps) is not very accurate, and results in strange-looking pixels or odd colors sometimes.