what makes red tomato sauce turn orange in colour?
Update:

It's been a few years but there now is a definite answer to this question.  

@PegDat is correct.  The Tomatoes Oxidize when they are exposed to air and turn orange.  

This was proved using an experiment with vacuum blender  blending tomatoes with air and with most of the air pumped out.  

When you reduce the air in the blender chamber, the tomatoes remain bright red.