Due to collectively low intelligence, wisdom, and charisma, combined with a tendancy towards chaos, it's understandable to see red slaad as little more than animals. The irony of this is that even animals have more wisdom.
Red slaad, therefore, are likely to be somewhat mad. They're easily distractible, paranoid, mutter to themselves, and in general act schizophrenic. This combined with their strength means they take offense easily and are likely to lash out at threats, real or percieved.
The only thing that boosts a blue slaad is that they have average charisma. That means while red slaad are generally inarticulate and rarely speak (at least coherently), blue slaad are quite capable of expressing their demands, at least in Slaad. Of course, these demands tend to boil down to "Food, kill, eat, purple." They're still dumb as a bag of hammers, and completely self-absorbed, so even if you can understand them they're likely to ramble, get off topic, and forget things easily.
Anyway, green slaad have average mental stats and good charisma. They're perfectly capable of carrying on a completely articulate conversation, planning ahead, and understanding most concepts if explained or experienced. Unfortunately, they don't seem to realize their own limitations. They have strong personalities, which often makes them seem smarter than they are (and they believe it). They assume they're right and like to boast about their own intellect. Best to just agree with them, rather than trying to prove them wrong. They also are not team players, being too fractious and self-confident to consider anyone else's ideas.
Given the options, it's no wonder Slaad is an unpopular language.
Gray slaad are worse. They know they're not as physically powerful than other Slaad, so they tend to have elaborate schemes. Their high intelligence, wisdom, and charisma make them natural schemers, weaving intricate webs of deception with multiple minions, all with the goal of furthering their arcane knowledge. They are chaotic despite their tendancy to use intricate plans because their plans often involve much deciet, infiltration, and subversion, often destroying institutions or formenting rebellion, often with the goal of seeing what the effects are. They still have no social skills, though, so attempts at dealing with others still tend to be crude and without finesse at best.
Death Slaad have become corrupted by evil. In their arcane research, they have happened upon forbidden knowledge and secrets. Other Slaadi can sense their corruption, but they often live in fear of the Death Slaadi. Death Slaad, as their name implies, enjoy causing death and destruction. For other slaad, such things are merely a byproduct of their life cycles or pursuit of power, but for death slaad it is a goal. But they are frightfully intelligent, keenly perceptive, and frighteningly articulate. They rarely use their intense charisma for anything except scaring the bejeezus out of anyone they meet, as most creatures can see the darkness burning within.
Oh, and for epic slaadi:
White slaadi are somewhat like a return to form after the death slaad phase. If asked, they will treat that portion of their life cycle as being young and foolish, not understanding the true nature of chaos. Indeed, they do have a keen understanding into the "true nature of chaos." They can speak on end, perfectly explaining why a state of utter entropy, of world without form and age without time, of infinite possibilities existing simultaneously and at the same time not existing at all, why all of this is far superior to a formed world. They also have a disturbing insight into what people are thinking, able to form their arguments perfectly almost perfectly to prove why chaos is superior.
Of course, they are also completely insane. Time spent around one will prove this fact. And yet, in some ways, what they say makes a lot of sense...
Black Slaadi are disturbing to even look at. They are like a hole ripped in reality, a black void in the shape of a monstrous toad. They speak with utter certainty in the voice of entropy itself, not so much using words as using their absence. There is no reasoning with them, no fooling them, no understanding them. Even other slaadi find them a bit extreme, since while other slaadi wish to merely bring down institutions or people, black slaad wish to destroy the universe itself.
How's that?