In the real world, the RX-78-2 and the other Project V mobile suits were decked out in a Toyetic paint scheme to sell the show to kids. In-universe, they were prototypes, and prototype jet fighters in the 1970s and 80s were painted in similar bright and bold colours. Here's an example.
Why do Zeon mobile suits always have that one red eye? It's a Visual Pun of sorts on how they never seem to win. In Japanese culture daruma dolls are used as a sort of good luck charm to wish for success in an upcoming endeavor, like studying for an exam or running for political office. You paint on one eye when you start and the other when you succeed. The implication is obvious.
By choosing to use colonies instead of the planets, the writers cleverly sidestep the research work needed to make terra-forming seem scientifically plausible.
At first glance Lalah's cheerful appearance seems out of place, considering her past is similar to that of another young lady. But then it's revealed that the Flanagan Institute considered her their star student and she was subjected to testing out Newtype weaponry, and later in Mobile Suit Gundam: Char's Counterattack Char reveals he regrets using Lalah like a machine. Adding this together, it begins to sound very similar to a certain girl in Mobile Suit Zeta Gundam who was a Newtype guinea pig for weapons and subjected to massive amounts of torture and Mind Rape, while displaying an identical cheerful disposition that seemed off. No wonder Lalah seemed happy after she died.
Let's not forget that, before being taken in by the Flanagan institute, Char found Lalah in the streets. Who knows what kind of life she left back then.
According to the manga adaptation Gundam: The Origin, Lalah was working for an abusive man who forced her to use her power to cheat at the roulette and similar things, and was beaten quite often.