Why does my video look washed out after export from Premiere Pro? (Rec.709 issue?)

This is a classic issue! The problem is likely that you're not applying the proper S-Log3 to Rec.709 conversion. When you just apply a basic Lumetri correction, Premiere doesn't automatically convert the gamma. You need to use the 'Input LUT' in Lumetri under 'Basic Correction' and select 'SLog3-SGamut3.cube' from the Sony category. That will properly map the log footage to Rec.709. If you're already doing that, then check your export settings: under the 'Video' tab, make sure 'Color Space' is set to 'Rec.709' (not 'Rec.2100 PQ' or 'Auto'). Also, ensure that 'High Dynamic Range' is unchecked, because if HDR is enabled, it can cause washed-out output on standard SDR displays.

Great point about the LUT! I also want to mention the full vs. limited range issue. In Premiere, when you export H.264 for YouTube, the default is 'Limited' range (16-235) which is correct for broadcast. However, if your project is set to 'Full' range (0-255) and you export with limited, you'll get a slight lift in blacks. To fix this, go to Project Settings > General and check 'Video Range' – it should be 'Limited' for delivery. But more importantly, YouTube applies its own color processing, so even if your export looks correct in VLC, it might shift slightly. Try exporting with the 'Match Sequence' preset and then re-upload – sometimes the difference is minimal, but if it's washed out, it's likely the LUT or the HDR flag.

I had the same issue with my A7S III! It turned out I was accidentally leaving 'Rec.2100 PQ' as the color space in the export settings because I had previously edited an HDR project. Make sure to set 'Color Space' to 'Rec.709' and also check the 'Gamma' under the 'Video' tab – it should be 'BT.709'. Also, a quick tip: in the Lumetri panel, under 'Creative', you can adjust the 'Faded Film' slider – if it's not at 0%, that can cause a washed-out look. But since you said it looks fine in the source monitor, it's probably not that. One more thing: check your sequence settings – if your sequence is set to 'Rec.2020' (common if you imported HDR clips), that will mess up the colors. Set it to 'Rec.709' and re-export.

Thanks everyone for the detailed responses! I checked my export settings and indeed, the color space was set to 'Rec.2100 PQ' – that was the culprit. I changed it to 'Rec.709', applied the proper S-Log3 LUT, and the export now matches the source monitor perfectly. Also, I made sure the video range was limited. I've re-uploaded and it looks great on YouTube. You all saved me hours of frustration – much appreciated!