Are you viewing the media on a properly calibrated external TV? If not, then there's just no way to know if you're seeing the signal accurately, and hence no way to know if there's really a problem.
No need for a calibrated monitor if he's comparing two versions of the same shot side by side (and there's always the histogram view if you need numbers to back up your eyes).
To clarify is the 'dark' effect seen in the final media file after Pr exports the sequence or only in the program monitor?
As Dave notes, I'm looking at the two versions of the shot right next to each other in a timeline.
I haven't taken the two shots through to a final export, so I don't know what effect that will have. I'm seeing the discrepancy in the Program monitor in the GUI and in an external monitor (good but not pro-calibrated), and in the reference waveform monitor, on which it appears that, compared to the clip rendered in Speedgrade, the clip with the effect applied in Premiere has similar "white" levels, but the darker levels are stretched downward, for example something at 10 units in the Speedgrade version is at 5 or 6 units in the Premiere effect version. Visually, don't see an obvious shift in color balance, just in the brightness, especially in the dark areas.
Here's a split screen export from the program monitor, the upper part of the screen shows the .look file applied in Premiere. The lower part of the screen shows the file rendered out by SpeedGrade, then imported into Premiere. The lower portion is consistent with the way it looked in SpeedGrade. The top portion is darker than the way it looked in SpeedGrade. This image was exported as a JPEG to meet the file size limit on the forum, hopefully the JPEG compression hasn't messed up look too much.
I'm not sure if you still have the same problem but I've noticed that certain LUT's that you can find in Speedgrade can help match the two programs and the way they display the image. Also I've realized the "Input Saturation" setting DOES NOT translate well into Premiere.
1. Take a grade you made and turn the Input Saturation up quite a bit for that specific grade..
2. Create a separate .Look file with that grade.
3. Turn the Input Saturation back to default and make a separate .Look with that grade.
4. Switch between the grades from Step 1 and Step 3 to see if it better matches your Speedgrade image.
Note: If these still don't match, what matched my two programs almost perfectly was using the DAY4NIGHT - SL - 3527.itx LUT in the Speedgrade options under: Timeline > Setup at the bottom. Use this LUT in conjunction with Steps 1 through 4. Experiment with different LUTs.
I hope that helps! :-)