[pygame] Unwanted blue pixels at edges of antialiased circles

[Marian Steinbach <marian@xxxxxxxxxx>]

Hi!

I'm new to pygame and just used it for the first time for data
visualization. See the result here: http://vimeo.com/26157684

The visualization consists of anti-aliased dots in various shades of
gray on a purple background.

Dark grey dots have unwanted blue pixels on their edges, which I
cannot explain. You can see them especially in the upper part of the
video.

Here is what I'm doing to draw the background and dots:

# canvas
screen = pygame.display.set_mode((width, height))

# background
self.screen.fill([47, 40, 54])

# dot
radius = 4
color = [64, 64, 64, 255]
pygame.gfxdraw.aacircle(screen, x, y, radius, color)
pygame.gfxdraw.filled_circle(screen, x, y, radius, color)



Any ideas where the blue pixels come from?

Thanks!

Marian