FFmpeg does not preserve colors after resizing
Ad 1:

Try adding the -pix_fmt yuv420p10le option (e.g. before -vf). Or only -pix_fmt + for using the same pixel format as the input video has.

If it doesn't help, you obviously have an inappropriate, albeit more common FFmpeg version — only for 8-bit colors. (Your original video uses 10-bit colors, and FFmpeg will try use the best 8-bit pixel format in this case — with the colors' degradation, of course.)

FFmpeg may be built for 8-bit colors or for 10-bit colors, or — in recent time —  for both of them (for your HEVC encoded video). 

So you need to build (or obtain by other way) version for 8-/10- or 10-bit color depth. 

Ad 2:

Bitrate of 1700 is very low — only 1700 bits per second, i. e. about 212 bytes per second. 

To reach such a low bitrate and at the same time reach your 23.98 frames per second, the encoder is limited with  average size for 1 frame about 212 / 24 = 9 bytes only! 

Did you see a picture of such small memory? It has almost no information, so the gray image.

You probably wanted 1700k (Kilobits per second) — or, more probably — 170k:

-b:v 170k


so correct your command in this way.



Addendum to Ad 1:

You use the (default) 4:2:0 chroma subsampling (with inevitable color and contrast degradation).
Try the maximum quality, i.e. 4:4:4 (no subsampling), or — if it will be sufficient for you — 4:2:2.

To reach this, use -pix_fmt yuv444p10le and change the video profile to main444-10 (with option -profile:v main444-10).