Tree structure folder icons should be gray[500]

[daileytj]

Describe the bug

Tree structure folder icons are black[500]

What is the expected behavior?

Tree structure folder icons should be gray[500]

What are the steps to reproduce?

1. start design patterns project and navigate to the Lists/Tree Structure example
2. inspect folder icon and observe that it is the wrong color

Screenshots or links to minimum reproduction example

Environment

Anything else to add?

[emclaug2]

Fixed in #244