[b]Blue is a constraint. If it's in the translations in the channel box, then it's a point constraint. If it's in the rotations, it's an aim constraint. If it's in the scale, then it's a scale constraint.
Gray is locked
Light Gray is non-keyable
Muted is brown
Blended is Green, means it's controlled by a constraint and keyframe for example
Light Orange is keyed
Purple is that an object is controlled by an expression, like through the expression editor
Yellow means it's connected to something, through the connection editor for example
You can find all of these by searching "channel box colors" in the maya help and clicking on "All About: Channel Box" In time you learn all of these, especially if you do a lot of rigging.[/b]