At runtime, if I change the VCL Style to a style that changes the color of the background of the THtmlTreeView it changes fine, however if I then select the default VCL style of Windows, the background of the THtmlTreeView does not get reset and continues to show the color of that previous VCL style.
Just noticed that it is not just the background color that sticks, all the VCL Style attributes remain from the previous VCL Style once you change to the default Windows style (i.e. no style).
We have investigated this and seen the issue.
A fix is applied. The next update will address this.