Transparent text objects can be a handy tool to prevent end users from drilling down on expression data in charts or graphs.
We have an application with a straight table that has 6 dimensions and 3 expressions. We have changed the labels on the dimensions to user friendly names in the chart settings. Many times end users would select a value in the expression column and it would drop all of the original dimension names in the current selections box. This was both confusing and rendered undesirable results. To overcome this, we created a transparent text object to cover the expression values so that the end user could only select and filter by dimensions.
Please review the attached QVW for example for both charts and straight tables and using a button to toggle object on and off
Here are a few screen shots for high level explanation
You need to make sure you select top layer in the text object properties before you move your object. If not, your object will disappear behind the object you are trying to cover when you place it. Size the text object so it completely covers the selectable area of the chart
And then you can choose whatever color you want and adjust the transparency level with the slider
This works best with objects that have a fixed size. You likely do not want to use this on a container object