Which box have you received? The Netgem 4k one or the TalkTalk TV Hub.
I found my Hub box was too bright in colours as it was trying to upgrade the picture to 4k.
I was able to correct this by adjusting the TV picture mode. Perhaps you can improve this by doing the same?
Your HDMI cable may not be connected properly. Did the box come with a lead and have you used this or one you already had on your own box? Use the one provided or if you are try unplugging it and reversing it. Sounds silly but it does sometimes work.
If it's the TalkTalk Hub, there are many various picture output modes in settings. The box should select the most compatible mode for your TV but it may be it didn't for some reason. Make a note of the setting used before having a play to see if this makes any difference.
If these changes don't help, reset the box and see if that makes any difference.
Let us know how you get on.
Please remember to mark Solved Posts with Best Answer. Doing so helps other customers and saves TalkTalk's Support Team time by only looking at unsolved topics. Thanks, Steve (a fellow customer).
