I used real grass - dried and sprayed with hobby varnish. It was a little bit difficult to glue it on the paper, but finally I suceeded.
The butterfly was initially ivory, but I painted it to fit the required colours.
As neutrals are allowed, I used black leather-like textured cardstock as a base and ivory glossy paper to glue the grass on.
The blue thank you tag was the final touch ... and this is it: