brown substance without UV/VIS spectra

[JackBean]

This is rather chemical/physical problem, but maybe someone of you may have some suggestion.
The thing is we have a substance isolated from plant being white, the spectrum has two maxima in UV (<300nm), but when the substance was synthesized by chemists, it is brown. However, the spectrum is exactly the same with two maxima in UV, but nothing in visible part of spectrum.
I was thinking about some impurities or mechanical particles, but all that should absorb (or diffuse) the light, right? What about particle size? But the solution is brown as well. And if you see it by eye, you should see absorbance, right?

What could be the reasoning?