The green colour of chlorophyll is simply being masked by one of a number of other pigments not involved in photosynthesis, including flavins and carotenoids, which are present in abundance in certain species of plant.
Carotenoids are yellow and orange (they give carrots their orange colour, hence their name) or orange/red in colour, so probably contribute to the red colour of leaves, but the richness of the red colour is provided by flavins. These are a group of photoreceptor chemicals which absorb blue wavelengths of light from the spectrum of wavelengths present in white light and emit all other wavelengths, making the pigment appear red. This blue light controls several reactions in the plant, including the biosynthesis of pigments, carbohydrate and protein metabolism and photomovement (growth movements of plant shoots and roots in response to directional light, gravity, and so on).
The assumption that chlorophyll is green is a correct one, but leaves have a number of colour pigments in them, hence when the chlorophyll decomposes in autumn, they turn a variety of other colours. Very strong colours mask the green of chlorophyll, but photosynthesis still takes place (red, brown and even blue seaweeds photosynthesise). Trees such as you describe are "sports", nursery creations grown for show. They are less efficient and in the natural world would be very scarce as trees with green leaves would easily out-compete them.