Thank you for your question.
No type of oil will cause a false positive in the hormone detection ampule (D). Only steroidal hormone will cause the purple reaction, that is indicative of a positive identification.
The way the test works, in the instance of testing for testosterone, is that ampule B is used for ester identification (esters are fatty acids/oils) and ampule D is used for hormone detection.
Carrier oils can cause a reaction in ampule B, as it is looking for esters, which are fatty acids/oils. In the instance that you see a reaction in B, but D does not turn purple, this would be a negative identification where only carrier oil is presumed to be present and no hormone has been detected.
All the best!