Forsythia to me is spring and this bunch of faux Forsythia brings spring to your home like no other flower can.
In this picture the stylist has gathered a few tall branches en has arranged them in a Delfts Blue vase. The perfect combination if you ask me. Our great imitations of these forsythia branches look the part and have a metal wire in them so you can bend them in any way you want. This way is is easy to mimic the arrangement in the pinterest picture.
If you want to add another colour, by all means. I’d suggest something in blue or pink. Or maybe put a bunch of bright red tulips in a vase right next to it.
Mix and match is what I’d say.