Downloaded a couple of 4K titles but the colours are very dull. Is that a HDR issue with Infuse at the moment?
Yes, HDR support is currently in the works for 5.5.6.
I find that if a 4K title is BT.2020 colour gamut (eg from VISIONPLUSHDR) it will always have dull colours while titles in BT.709 will be fine. I suspect my LG OLED doesn’t like that colorspace. My solution is to avoid 2020 titles.
To check the colorspace medainfo (MediaInfo - Download) is very useful
HDR titles use the BT.2020 color space.
So, if I understand well what James says, they should work in Infise.s next version 5.5.6.