Happy Color sharing using Apple One Subscription

Not an app I am familiar with, but a quick look at the page for it - https://apps.apple.com/us/app/happy-color-art-coloring-book/id1407852246 - suggests that the app is free, with in-app purchases to remove ads and unlock other features. Those purchases won't be sharable.

tt2

If it was an Apple Arcade app then it would be ad free, and contain no in app purchases. You can still use the main app store when you have a subscription to Apple Arcade or Apple One. Each app's page in the store will tell you whether that app is eligible to be shared within a family, and whether or not it offers in-app purchases. In-app purchases are not normally (ever?) shared.

tt2