ofSetColor's alpha to equal num_pts

Here’s what I’m trying to do…

Let’s say I have a limit of 500 num points. When I draw 1 point, I’d like the alpha to be 255. When I draw the final 500th point, I’d like the alpha to be 0. Of course 255 is < 500. I thought I could achieve this via an if statement, similar to:

  
if (NUM_PTS == 0) {  
		ofSetColor(255,255,255,255);  
	} else (NUM_PTS == 500) {  
		ofSetColor(255,255,255,0);  
	}  

But this didn’t work.

If I figure this out, I’ll post my solution. Thank you!