Colorize neural filter - how to zoom in when selecting an area for manual coloring?

You could also use the Colorize filter as a starting point and use other methods of adding color. Here's one approach:

1. Make new layer
2. Use a selection tool (such as the Object Selection Tool) set to Sample All Layers in the Options bar (Window > Options) to select where you want a particular color applied
3. Select the color you want to apply
4. Fill the selection (Edit > Fill)
5. Set an appropriate Blend Mode at the top of the Layers panel (try Overlay or Soft Light)

The Colorize preview where you can add focal points for color doesn't enlarge, but you could click on the "No" button at the bottom of the filter if you're not satisfied with the results and provide the feedback to the Photoshop team that you'd like that preview to be larger.