I've only used tren from 2 different UGL's. The first lab produced a very dark, rusty colored tren. The oil seemed very potent, I gained a good 20lbs on cycle and set all kinds of PR's. I ordered 14 (10ml) vials between 2 orders. The color of the oil actually changed to a lighter color in the 2nd batch because the brewer was having complaints of too much PIP, and switched to another oil base (not sure which) but the tren was just as effective.
The 2nd UGL produced tren that was a little lighter in color, more like the 2nd batch of the first UGL, and quite frankly I dont think its the same quality as the first (and the price was reflective of that). It still did its job, but just wasnt as good.
So my .02 cents is, the color doesnt matter. You have to find out if your source is reputable and then experiment for yourself.
Hope that helps!