Issues with color fill on basic art canvas

Hello. I am attempting to use the fill with color block to properly color shapes, but the feature does not appear to be working as intended. I can create a square but when I add the block for fill with color, it will either change the border color of the square or do nothing at all. I tried running this project in grid squares and I am able to fill any square with a color, but it does not work in art canvas.

What am I missing? Is this feature not available in the basic version of art canvas? We have significant problems running art canvas+ in class as our chromebooks cannot upload images. I have been troubleshooting and trying alternatives for a couple of hours now and just cannt get this feature to work.

def when_started1():
drivetrain.set_drive_velocity(100, PERCENT)
drivetrain.set_turn_velocity(100, PERCENT)
drivetrain.drive_for(FORWARD, 300, MM)
drivetrain.turn_for(RIGHT, 90, DEGREES)
drivetrain.drive_for(FORWARD, 300, MM)
pen.move(DOWN)
for repeat_count in range(4):
drivetrain.turn_for(RIGHT, 90, DEGREES)
drivetrain.drive_for(FORWARD, 600, MM)
pen.move(UP)
drivetrain.drive_for(REVERSE, 200, MM)
drivetrain.turn_for(RIGHT, 90, DEGREES)
drivetrain.drive_for(FORWARD, 200, MM)
pen.move(DOWN)
pen.fill(255, 0, 0, 100)

I was able to use the feature in art canvas after first painting the entire playground white. I suspect the issue is that the art canvas is seen as a transparency and the fill with color block will not work on a transparency.

Seems like a significant oversight