The problem can't be determined from those four lines, you'll have to post the whole code

We also need to know whether variables distance & dropRate are of integer or fractional data-type.
In case they are of integer type, that line -> dropRate = 255/distance;
would result in zero when distance > 255.

Also, I guess you need to relate 255 max green color tone to that of total canvas height.
In a way in which some amount of height corresponds to 1 decrease of green or something like that.

That's my 2c!  

@GoToLoop g, dropRate and distance are all float values and yes i need the g to decrease at the rate the shape falls so that by the time the shape hits the bottom of the screen, the shape is fully red.

This is a fairly common thing for beginners to program... I wouldn't worry about plagiarism. We have to make guesses as to what kind of mistake you made if you don't post the code. At least you should post the four lines with an ellipse(), how you set up fill(), and where they appear in draw() / whatever function.