LOL!! Heruga, you crack me up with your requirements for your plants :-) They are not pieces of furniture and do what they do as they please.....not exactly static beings. You would find things so much easier if you'd just go with the flow. But we've had this discussion before :-))

Check out M. sinensis 'Silberfeder'. The name means 'silver feather'. The flowerheads emerge with just a blush of pink - barely noticeable - and then turn silver and remain silver. The foliage also doesn't develop much color in fall - unusual for miscanthus - just turns a dusty straw color. Gets pretty tall though, so plan accordingly.

That's about as close to a pure silver as you are likely to get.

Thanks. I was actually looking at silver feather before posting this but I saw some pics of it being pinkish or brown in them so I got slightly confused. But I guess this ones the closest it can get. Btw I'm actually trying to assemble plants with flowers of all basic colors. The colors are red, yellow, white, green, blue, brown, pink, purple, orange, black and finally silver. I have every color except silver which is why I ask this

I suspect that what you are looking for -- no change of color in the fall -- is physically impossible, at least in a non-tropical climate. In the fall photosynthesis drops off, the plants lose chlorophyll and then other pigments become visible -- anthocyanins, carotenoids, etc.