What did you do?

Draw a rectangle with a color with opacity < 1 for border (e.g. outline='#0000ffaa')

What did you expect to happen?

The border color should be homogenous, and not altered by the fill color, if set.

What actually happened?

The border color is different in the corners, probably due to overlapping line segments.
Moreover, when a fill color is set, the border color is changed due to the overlap of the border and fill rectangle.

What are your OS, Python and Pillow versions?

• OS: Windows 10
• Python: 3.8
• Pillow: 8.0.1

Example

Code

import PIL.Image
import PIL.ImageDraw

image = PIL.Image.new(mode='RGB', size=(500, 500), color='#ffffff')
draw = PIL.ImageDraw.ImageDraw(image, mode='RGBA')
draw.rectangle(xy=((100,100), (200,200)),
               fill='#ffff00',
               outline='#0000ffaa',
               width=10)
draw.rectangle(xy=((205,100), (305,200)),
               outline='#0000ffaa',
               width=10)

image.save('image.png')

Result

Related Sources