Q.oleander
I have an oleander plant in my backyard that has white AND pink blossoms on it. Is this unusual or common?

Your Oleander is likely a grafted plant.
They are often sold with 2 colors and even tri-colored flowers on the plants.
Remember to keep children and pets away from a Oleander and use protective clothing when you work around the shrub. All parts of this plant are poisonous.
https://www.gardeningknowhow.com/ornamental/shrubs/oleander/oleander-growing-tips.htm