The traffic light system is totally useless for carb counting - it doesn't show carbs at all.
I find that the net carbs is the one to calculate by - the carbs minus fibre which is what we have in the UK, as in the US they have total carbs including fibre, which makes some usefully fibery low carb foods look too high.
I usually try to stick to 10 percent and under for everyday foods, and 20 percent as the absolute maximum for carefully portioned foods - those would be grapes and chocolate - or they should be - the 'oh well might as well finish the box/bar' fairy sometimes visits and vanishes them away when I'm not looking. Honest.
When just starting out I used to have a notebook - the paper kind, with alphabetical pages, listing the acceptable carb containing foods and their approximate values, and I also had a couple of different shopping lists, so that I did not get bored with the same thing every week - I still only buy tomatoes when I have run out of mushrooms and vice versa.