Yes, the new Streamline Player introduced in version 6.0 allows you to customize colors of every element of the player including background colors and button and label colors. To customize player sidebar colors please do the following:
Click Publish on the iSpring toolbar.
Select the Advanced Player template from the drop-down list and click Customize
In the customization window, select Colors in the top left corner.
Scroll down the sidebar to the Side Panel and Tabs groups of items where you can customize sidebar colors.
If you click the color icon to the right of the object, you will be able to adjust color of the item.
You will immediately see the result of customization in the Live Preview on the right. Once you’ve finished, click OK.