The RGB
mode is expecting 8-bit values, so just casting your array should fix the problem:
In [25]: image = Image.fromarray(pixels.astype('uint8'), 'RGB')
...:
...: # Print out the pixel values
...: print image.getpixel((0, 0))
...: print image.getpixel((0, 1))
...: print image.getpixel((1, 0))
...: print image.getpixel((1, 1))
...:
(255, 0, 0)
(0, 0, 255)
(0, 255, 0)
(255, 255, 0)