RGB led driver maximum current
a) They generally look white if mixed with same duty factor. Later you may want to change the color temperature of "white" by playing with tr, tg and tb.

b) LEDs are over-driven to compensate for low brightness due to multiplexing.
Thus you can overdrive them by a factor of 3 if the duty factor is 1/3.
However, they have a specification for the maximum pulsed current.
In your case, look into the datasheet if you got one.
Otherwise, give it a try and keep an eye on their temperature while over-driving them with maximum allowed pulsed current.

1A pulses should not be a problem.