Corrected comments

[radarhere]

If you look at this code

Pillow/Tests/test_file_gif.py

Lines 411 to 420 in 3d2f3ba

	# 4 backgrounds: White, Grey, Black, Red
	circles = [(255, 255, 255), (153, 153, 153), (0, 0, 0), (255, 0, 0)]
	im_list = []
	for circle in circles:
	img = Image.new("RGB", (100, 100), (255, 0, 0))
	# Red circle in center of each frame
	d = ImageDraw.Draw(img)
	d.ellipse([(40, 40), (60, 60)], fill=circle)

it is apparent that the comments are not accurate - circles is not the background color of the image, and the circle being drawn in the middle is not always red.

This PR updates the comments to fix that.