Yup, HDR+ is a must for low light. I am not seeing purple cast so far, not sure. Took those pics under room lighting condition, not very bright.
https://www.reddit.com/r/Android/comments/6t4i0x/google_camera_with_hdr_ported_to_snapdragon/
The person Aucread on that thread also mentions purple on G6 when trying the HDR+ in low light
Oneplus owners seem to have the best experiences with the app, though not sure is it due to statistical number of oneplus owners who tried the app