They'd likely all evolve to be green.
Plants aren't just green because their ancestors are green. Plants are green because, in most environments, being green is more advantageous than being red.
The leaves of green plants tend to be dominated by chlorophyll, while those of red or purple plants have a different pigment called anthocyanin. Plants have evolved to produce both of these pigments, and generally whichever pigment is more beneficial for survival in a given environment is the one found in plants in that environment.
If there existed plants that ancestrally used a red pigment, like anthocyanin, it's likely that they, too, would evolve the ability to produce a variety of different pigments, some of which would be more useful than others in some environments. Most plants would probably be green, regardless of their ancestry, because chlorophyll is more efficient at converting light into energy, in most environments.
If, unlike plants, our new red organisms couldn't produce photosynthesis, they'd probably die out. Chlorophyll-based plant life is dominant on earth because it's the most efficient, and non-chlorophyll based life would likely be unable to compete with it in most ecological niches.
Interestingly, there's a hypothesis that green plant life wasn't always dominant on Earth. The Purple Earth Hypothesis states that retinal-based photosynthesis evolved first, but that retinal-based organisms were unable to compete with plants in most ecological niches. They still exist, though not in great numbers, with haloarchaea being the prime examples.