What you're seeing above is what the app looks like once you open it (in the case above, on an iPad). I'm going to quickly run through the options you see on screen.
For starters, I'm pointing at some hand sanitiser (ignore that terrible brand name). That small white circle-outline on the right side of the bottle is the actual colour picker. I can either move my camera around, or move that circle around with my finger. When I do, the colour (in this case, "Persian Green", updates automatically), it even gives you the hex code (#01B5A3).
Since the camera is constantly moving, you're able to freeze the screen (check out the snowflake icon on the bottom). This lets you freeze the screen, and therefore the colour, wherever the colour-picker currently is.
You can save each colour you pick in a "colour library", for future use. You can enable your phone's flashlight (lightening icon) for night-time use. You can even enable colour-blind mode (so in the example above, instead of "Persian Green", it would just say green).