color: move the 'colorlabel' function in the core module The extract code is relocated in core.

color: extract the label code into its own function We extract the logic into a function. This will allow us to move the logic into the core 'color' module and later call it directly from core.

color: inline the 'showlabel' method This function is quite simple and only have one call site… located a handful of line under the definition. We inline the function for the sake of simplicity. One of the motivation to do that now is that it reduce the amount of new method we will have to add to the core 'ui' class for color support.

color: move '_colormode' to the core 'ui' class Having all 'ui' objects aware of 'color' allows us to update the core code to handle color. The mode will stay 'None' in the default case so that will not introduce any changes.