I have bought some stained glass window panes for the small sections of my main front windows. The green parts are too vivid and don't match with my decor. I didn't know that it would have this effect. Is it possible to have just those green parts taken out, restained to a lighter colour, then placed back into the same window panes?
Assuming it is actual stained glass,the colour is part of the glass and cannot be made lighter. You could take the panels to a stained glass artist,and it may be possible to have the offending coloured pieces removed and replaced. This will require re-leading. TBH,I don't have enough knowledge of the construction of leaded/stained glass to say if this is possible. It may depend on whether it is modern or older glass.
Go to a craft shop like Hobbycraft.
They have 'cellophane' A4 sized (possibly bigger) sheets and you can cut to fit. I would pick either blue or yellow on top of the green and it will give it a different shade. They're not expensive and you can play around until you get a colour that you like.
You just have to work out what to stick it on with. Ask in the shop?
Look on the Internet for Fablon. You can get all colours and many textures, including transparent and semi-transparent. This has the added advantage of being sticky-backed. You could buy a light grey semi-transparent plastic film, maybe and even try two or more layers.