Foliage weird rendering


I made some grass using Speedtree and then i import it to unreal 4.20, and used it as foliage, now i have 2 issues

1-the foliage always green though the texture is yellow
2-when i hit build, some of the foliage is black the rest casting no shadow and have a green color instead of yellow

-i checked the double sided in both the material and the mesh
-i checked light map resolution in the instance settings, cast static and dynamic shadow also checked

can someone tell me how to improve the built shadow quality please ?