The Mark III has a lot of noise in the shadows (high read noise) at low ISOs. 500 ISO is a digital push, brining the blacks up. Cinestyle further raises the blacks.
This looks underexposed. Did you meter correctly? Not in-camera but through an incident meter. The internal meter is not accurate for cinestyle. Looks nicely lit and composed, but the underexposure will get you. HTP further exacerbates this issue, and it's there to some extent on all Mark III video, even raw.
I think I have the same problem.
I had been playing with Marvels Cinestyle..and early test seemed to show if I slightly underexposed I had lots more room to try to use Resolve to bring up exposure, and get good color saturation, etc.
I'd gone through my whole video on Davinci Resolve (edits done on FCPX), and it looked great.
I brought it back to FCPX...and most of it looks good, except anywhere with dark/black is highly noisy, I mean really bad.
I can't seem to find a happy medium. When I exposed in camera for proper exposure, it always seems things get blown out, so, I tried underexposing by about 1 stop on everything...but now full of noise.
I didn't think the 5D3 had noise problems till you got in high ISO? Or is that just with stills?
I shot everything in multiples of ISO 160, trying to keep it below 800 -640 as a last ditch high value...most of it was 480 and below.
this is getting frustrating, I desperately want to try to shoot with a cinestyle and learn color correction and color grading, and get great images like I've seen others get out of the 5D3, but I've not hardly gotten anything near what the baked in Canon Styles seem to result in....I just don't know what I'm missing.
I have all my lights matching color temp, I have decent lighting, good WB...and yet, my images look like they came out of an early edition iphone or something.