Which 'specific' points do you want to be different? Do you know which points in advance or does it depend upon the data itself?

For example, in a simple graph of x/y you might want every third point plotted in x to be a different colour (or the same colour) or values over y=10 to be different colours or values where x<5 and y>100 to be different colours...

If you can define the problem a little more clearly it shouldn't be too difficult to solve :D

I have an array of data in 2 columns. The points I want highlighted are larger than the numbers before and after them, and are larger than 0.65 times the largest number in the array.

This does the first part I think, but "and are larger than 0.65 times the largest number in the array." doesn't make sense to me.

1. int[][] myArray = new int[20][20];
   
   float largestValue;
   
   void setup() {
   
     largestValue=0;
     int r1, r2;
   
     randomSeed(millis());
   
     size(600, 400);
     for (int i=0;i<20;i++) {
       r1=int(random(1000));
       r2=int(random(1000));
       myArray[i][0]=r1;
       myArray[i][1]=r2;
       if (r1>=largestValue) largestValue=r1;
       if (r2>=largestValue) largestValue=r2;
     }
   }
   
   
   void draw() {
    
     background(0,0,0);
     analyse();
     text("Largest Value " + largestValue, 20, 400);
   
    
   }
   
   void analyse(){
      
     for (int i=1;i<19;i++) {
    
         fill(0, 0, 255);
         if((myArray[i][0]>myArray[i-1][0]) && (myArray[i][0]>myArray[i+1][0]))
           fill(128, 0, 0);
         text(myArray[i][0], 20, i*20);
   
         fill(0, 0, 255);
         if((myArray[i][1]>myArray[i-1][1]) && (myArray[i][1]>myArray[i+1][1]))
           fill(128, 0, 0);
         text(myArray[i][1], 60, i*20);
   
     }
    
   }
   
   

Hello,

"and are larger than 0.65 times the largest number in the array."

The rough idea is you mark only those numbers that are pretty big compared to the biggest number you have.
Precisely that are bigger than 65% of the biggest number. That makes about half of the value of the biggest number.


What to do
You do this only once, so do it in setup().
Loop the array, find the biggest number:

1.   int biggestNumber = -1000;
2.   for (int i=1;i<19;i++) {
3.       if (myArray[i][1]>biggestNumber)
4.          biggestNumber = myArray[i][1];
5.   } // for

or so.

Multiply it by .65 and store the result in a var biggestNumber65percent or so.

Then, when you do your if check in draw():

1. if (myArray[i][0] > biggestNumber65percent)

Greetings, Chrisir