I would like the option to color code pages and layers and objects (e.g., shapes, images, text, etc.) in the Page & Layer Gallery. This would be useful to informally and quickly organize content into groups in a way that it is easy to visually scan the list while working. This would be helpful if a person has many pages or layers or objects and roughly wants to organize content by theme.
Click image for larger version.  Name: 20171231_color_code_pages_layers_idea.png  Views: 137  Size: 36.8 KB  ID: 119690
For instance, if making a presentation with 60 slides that reports research findings from a study, it may be useful to group the slides into groups of Introduction, Literature Review, Research Design, Method, Results, Discussion, Conclusion. Or, if making a graphic or diagram, it may be useful to group groups of objects. For instance, let's say I am making a metaphorical graphic of business processes as a team of three people. Each person in the team represents a different business process. Each person is composed of a head, torso, and limbs. Each subdivision of a person is a group (i.e., person one's limbs objects are one group, and his/her head objects are another group, etc.). Each person is a layer. Each group of three persons is a team and each team is a group of layers. If moving around multiple teams, it may be useful to have them color coded so that it would be quick and easy to know which team is which.

Lastly, I use another application that offers such a color coding strategy for its layers, modo, and it is very useful. Please see the below image for an example from that system. Note that in this example, you can see both groups and individual layers color coded.
Click image for larger version.  Name: 20171231_color_code_layers_modo_idea.jpg  Views: 175  Size: 80.9 KB  ID: 119691
I hope this is useful.