Not sure if this is a bug or I am missing something. What is the Tick color selection supposed to change? For some reason I am not seeing any change on the chart when changing this option. Maybe I need to turn something off in the chart settings to see this change?
The Tick Mark Color property adjusts the color of the small line between the Tick Label and the chart itself. It does not adjust the grid lines on the chart.
If you want to make the changes more visible, I would recommend adjusting the Tick Mark Outside Length, and Tick Mark Inside Length.