You tune into a channel. The screen is completely green. Audio plays fine. The video is replaced by solid green. Your reseller's video decoder is missing a key component. The green screen is a fallback when the video can't be rendered.
A British IPTV reseller whose streams show green screens has an encoding problem. The video uses a colour space that your device doesn't support. The audio works because audio is standard. The video fails and defaults to green. The reseller never tested on your device type.
The British IPTV services that avoid green screens use standard colour spaces that all devices support. Rec.709 for HD. Rec.2020 for 4K is still risky. The reseller who uses unsupported colour spaces leaves you with green screens.
The IPTV reseller panel includes colour space settings. The reseller can choose standard or experimental. Standard works everywhere. Experimental might look better on some devices and fail completely on others. The reseller's choice reveals their risk tolerance.
The IPTV reseller UK operators who test on multiple devices would catch green screens. They'd switch to standard colour spaces. The resellers who only test on their own device don't know that your screen is green.
Here's a specific scenario that makes no sense. You're watching a channel. The audio is fine. The video is a solid green rectangle. You restart. Still green. You try different channels. Some are green. Others work. The green channels use a colour space your TV doesn't support.
You contact support. They say the channel works on their end. It does, on their device. Your device is different. The reseller never tested on hardware like yours. You're stuck with green screens on certain channels forever.
I've tested colour space compatibility across dozens of devices and resellers. Green screens happen when the reseller uses Rec.2020 or other wide colour gamuts. Many older and mid-range TVs don't support these. The safe choice is Rec.709.
A colour safe British IPTV reseller will have video that shows up correctly on your screen. You can test this by finding channels that are solid green. If any exist, the reseller is using unsupported colour spaces. If all channels show normal video, they're using safe settings.
The same principle applies to HDR versus SDR. Some resellers send HDR streams to devices that don't support HDR. The colours look washed out or weird. The careful reseller sends SDR to SDR devices and HDR only to devices that request it.
A compatible British IPTV service will have video that looks normal. No green screens. No weird colours. That compatibility comes from using standard colour spaces. Test on all your devices before you commit.