White indicates the areas that are not masked, and which will be included in the selection when the channel is loaded as a selection. However, you can reverse this order if you like. I have created a new channel mask on the photograph, this time creating various shapes with selection, and painting tools, and then filling them with white. If I double click on the Alpha channel's name in the Channels palette , its Channels Options dialog box will open. Darker areas are where there is more of the color.
Lighter areas are where there is less of the color.
Either way, the selection which results when the channel is loaded as a selection is the same. Here is what I got. The selection edges are also shown. The shapes were created with different tools which had different edge effects. I also added feathering to several, and anti-aliasing was selected for three of the forms.