Update hand-tracking-grab-controls.md

[ogreenaway]

Description: The schema for hand-tracking-grab-controls uses the property "color" instead of "handColor" as mentioned in the documentation.

Changes proposed:

• rename property in the documentation to match the JavaScript implementation

[dmarcos]

Thanks. We should probably rename the property to handColor instead. Seems more accurate. What do you think?

[dmarcos]

@ogreenaway If you want to change the property to handColor we can merge this. thanks