Well green cestrum is a weed and it doesn't grow here so can't comment on the seed colour. Cestrum nocturnum certainly has white seed and it can be a weed too though a highly fragrant plant. You could always keep one seedling in a pot and cut off the seeds before they ripen.

I have a Cestrum nocturnum in my garden and I just love the strong sweet scent given off at night. I have not had any experience of this species being a pest although other Cestrums certainly are. If you are worried about its toxicity there is a website (can't remember its name) that you can search by putting in the plant's name. This will give you the toxicity of the plant.

Andrew.

Hi Lucia,
I believe it is the berries of the cestrum which are toxic. I can understand your concern especially if you have children around, as they are somewhat attracted to berries.
Unfortunately there are so many plants which have parts that are toxic to people and/or animals (even some we grow in the vegie garden). If we started removing them all, we may not have much left! lol.
I really think the best thing is to educate children as young as possible about the dangers of putting anything in their mouth in the garden (or anywhere else for that matter).
Still, if it bothers you, then dig it out!
Cheers,
Dee.

Green cestrum is a declared noxious weed in Qld--its berries are black and very toxic ( in some shires it is mandatory to remove them because they poison stock )-- the leaves also smell like cats wee if crushed.. the flowers are sprays of small pale lemon colour and can smell nice at night.. They are very difficult to remove, drop their berries everywhere, which germinate freely, and send up suckers.. I hate them, and had nine ancient ones hanging over a dividing fence from a neighbour's side.Fortuneately the neighbour moved, and now there is only 1.