When you create the indicator for the output from the sub-VI it will not inherit the properties of the indicator in the sub-VI, and the sub-VI will not act on it in any other way than serve the data to it.
If you want the sub-VI to set cell colors of the indicator in the caller you'll need to give the sub-VI a reference to that indicator.
Feed that reference into a property node in the sub-VI and set the properties as you now do for the indicator inside the sub-VI (unless you ever display that indicator you don't need it to do anything with the indicator inside it).
The procedure will be as follows; Right-click on the indicator in the caller VI and select create reference, right click on the reference and create a control, paste that control in the s
ub-VI, associate it with a terminal...and wire the reference you created in the caller to that terminal of the sub-VI...now in the sub-VI wire the control to a property node, and select the properties you want to set...).
Here's an example as well:
http://sine.ni.com/apps/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3ED1D56A4E034080020E74861&p_node=DZ53012&p_submitted=N&p_rank=&p_answer=&p_source=External