[monolithed]

var array = ['rgba', {}], 
	expr = 'rgba(255,255,255,0.9)'.match(/[\d.]+/g),
	i = expr.length;

while(i--) {
	array[1][array[0].split(/\.*/)[i]] = expr[i];
}

alert(array); //array.toSource(): ['rgba', {r:255, g:255, b:255, a:0.9}]