I've recently learned from individuals more knowledgeable than I about such things that such files can have more than one standard for for color spaces. Perhaps the software reading your rendered Targa uses a different standard. If you have no other choice than to use Targa, you may be entering the often-confusing world of multiple color management:
thanks for getting back to me - strange situation! on my mac the thumbnails seem to display the correct colour, but the minute I open the file in photoshop, quicklook, preview etc, the image appears tinted blue-purple.
but seems to have sorted itself out - restarted after effects and no more trouble.. hmm!