If you eventually want purples/blues, you will want to add amendments and now is as good a time to start them. Follow the recommended frequency on the label and use a very good soil pH meter since the purples naturally occur in a very narrow pH range. The current color though is based on the pH of the potting soil since this ASB got planted in October and the roots have not had much time to venture much outside of the potting soil yet. Once they grow into your garden soil, they will show the correct soil pH color which is still pink as Houston soil is alkaline. But hopefully by then, your amendments will have started to acidify the soil. Aluminum sulfate should be applied in the recomended label amounts; too much can burn some of the tiny roots. Note: it would be easier to control the soil pH on a potted plant than on a shrub planted in the ground.