As a user, I should be able to select an entity color when creating Schemas and Types so that diagrams can be more easily followed

**Is your feature request related to a problem? Please describe.**
Problem is, diagrams get very wiry and hard to follow.

**Describe the solution you'd like**
It would be nice if a color picker could be included to highlight entities (background and or text and or border, etc)

**Describe alternatives you've considered**
Using System Designer as a playground and finalizing my UML using another software, or maybe Draw.io

No files, tests, or concrete entry points are named in the issue. Start by locating the Schema and Type creation flow and diagram entity rendering, then define how selected colors apply to entities and verify that the colors remain visible and make diagrams easier to follow.

Written by the indexing model from the issue text.