Well, unfortunately, you have to define what ``flat'' is. And I suppose it could vary from spectrometer to spectrometer. I'm not really familar with it on a practical basis, but that's the way it's supposed to be. Maybe SpectraLab has a logarithmic scale or it's weighted by frequency (so that white noise would be flat) or something? Maybe you can change it?

It should at least be a straight line or a very smooth curve, I'd think. Is it?

Edit: I guess the question is, ``What is the axis perpendicular to frequency measuring?'' If it's power, then it ought to be flat. If it's volume, it shouldn't.

Edit Edit: Here's a good overview of the different color-based noise names.