When using XAVC S codec from popular Sony cameras it appears that Premiere Pro decodes the footage to BT.601 colour space whilst other popular NLEs decode consistently with one another to BT.709. This means that anyone who records externally to ProRes (or others) will have an inconsistent image to the internal codec as the External version will be tagged in Premiere Pro as BT.709.

The metadata for the XAVC S contains an “undefined” tag for its colour space so I would assume that Premiere Pro would default this to BT.709 in accordance to the colour management system, not BT.601.
[Metadata from ffmpeg - Video: h264 (High) (avc1 / 0x31637661), yuvj420p(pc), 3840x2160 [SAR 1:1 DAR 16:9], 94726 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc (default)]

The TIFFs attached show the resulting shift in colour when compared to other decode methods