After having used the Chroma Key on the lower side of the pic you see the mask which only affects the green bar. The upper side of the pic is the source frame (a standard color bar). Or you need to use a 3rd party plug-in keyer such as the very good Chroma Keyer of Ignite Pro. Instead you could try using Color Corrector Secondary with its alpha mask option which often gives much better results than the legacy Chroma Keyer. Thus you probably just can't use that chroma keyer. And this is what seems to happen in your example. for clean green which will also affects cyan to turn blue. It cannot replace certain colors without shifting another color though looking at the black/white mask it seems to be perfectly separated. There is an issue/bug in the Vegas Pro Chroma Keyer since its first days.
