Orange-tip that isn't orange tipped

The twitchers are getting a bit twitchy about the siting of some Black winged stilts. I shall have to keep my eyes peeled for them. Meanwhile in the absence of the above mentioned here's a blip of a butterfly. 
Google informs me that this is a female Orange-tip, which can be differentiated from the male by the fact that it has no orange tips. So why are they all called Orange-tips? A bit sexist I think. 
The plant it is on is a garlic mustard which sounds more like a condiment and is apparently very tasty to the Orange -tip's caterpillars.