Not sure what you're confused about, and OP was talking about legal immigration.
Prior to 65 immigration act, California was over 90% white.
By 2010, non-hispanic white was down to %40, hispanic ~%37%.
That is a huge demographic change.
Hispanics nationally vote for Democratic/liberal politicians on avg. 70%.
So.. ergo, the dramatic blue turn California has taken politically can be accounted for by drastic change in demographics.
Your first statement is just restating the same premise: a dramatic change of the makeup of the electorate (whatever their "needs" or preferred political policies) changed the outcome of elections.
After Prop 187 about a million Mexican resident aliens got their citizenship. That also coincided with a hard turn towards fascism by the Republican party under Gingrich.
Immigration is part if it, and the other part is the Republican party's policies got too extreme for a lot of Californians. California Republicans were more like Schwarzenegger, who later in his term simply abandoned the Republican party. (I think he called Republican operators, crazy and unable to get anything done)
But only American citizens can vote. And I can't seem to find any data on the increase of the California population from naturalized citizens.