Do you mean you're using a powered Component to VGA transcoder?
Don't know about the 720p matter but as regards the purple (magenta?) tint that could be down to the transcoder, particularly if it's a cheap one.
I had a mild version of same sort of thing with a RGB SCART To Component transcoder used with a Dreamcast. It was simply due to a pot (variable resistor) on the green signal channel not being set properly.
I dialed out the magenta tint to get the colour balance to neutral and it's been fine ever since. Worked for me but it is only a suggestion about what might be causing the colour problem. The transcoder you're using may not even be adjustable in the same way.
If the transcoder has worked without the same fault with other devices chances are it is something else. It could easily be just a cable or connector problem. So you shouldn't fiddle with the transcoder until you're sure it can't be anything else and then only at your own risk.