What does cheat mode do and how can I activate it

The orange color means you have filled 75% of your storage for that resource (so you should be ready to spend them, otherwise you'll be wasting time and/or food). Kittens are considered resource by the game so it will always be orange colored

catpower and science have different color but they do not have any real meaning, they're only there to help you differentiate themselves from other resources. Later on you'll find a ridiculous resource when hunting, that will have orange color AND glow

Happiness goes down by 2% for every kitten you have after the fifth kitten (so the sixth kitten will drop it by 2% from 100% to 98%)

Happiness is the efficiency of your kittens. For example, a farmer (without any upgrades) normally will yield exactly 1 catnip per tick, but at 98% happiness they'll only yield 98% of that (0.98 catnip per tick)

Hunters can bring in items from the forest (I've only seen fur and ivory), each will increase the happiness by exactly 10%, cumulative (getting both increases by 20%). The amount of each of them only affects how long the bonus lasts, not how many the happiness bonus is

EDIT: Also, Amphitheaters reduces unhappiness by 4.8% each, which means that it will negate the happiness reduction effect by overpopulation, but can't actually increase happiness (so if you have only ever had 5 kittens, it will not increase the happiness)

EDIT 2: In reality, it looks like that as of v 0.9.6 Amphitheater does not actually reduce unhappiness by 4.8%. I have 18 kittens for a projected happiness level of 74%, unicorn raises it to 84%, yet 7 amphitheaters only brings it to 93%, about 1.8% each. I'll see if I can find more on this