That is going to require an update to the custom DTH to expose the Color loop (Flash and all the other extra functions of these bulb also fall in the same boat.) The CLI and Custom Capability and Presentations beta will bring the functionality to the app to allow this, BUT the SPECIFIC customization required (Custom Presentation that displays a button to implement a custom capability ‘color loop’) to make this happen hasn’t been released by the ST CLI team yet. (At least as of last check, devs can create the capability, but a command button wasn’t available in the UI at last check or at least didn’t work as expected)
If you’re technically minded and want to follow along - you can learn more about the CLI here: https://community.smartthings.com/t/custom-capability-and-cli-developer-preview