How to implement PCA color augmentation as discussed in AlexNet
You should not apply *255.

delta was supposed to be added to renorm_image, because you calculated this delta using cov, which was based on renorm_image. 

Then how would you restore renorm_image to your original image? *std + mean or *255?

Obviously you should apply *std + mean.

Therefore, 

delta = (delta*255.).astype('int8')
pca_color_image = np.maximum(np.minimum(original_image + delta, 255), 0).astype('uint8')


should be changed to:

mean = np.mean(renorm_image, axis=0)
std = np.std(renorm_image, axis=0)
pca_augmentation_version_renorm_image = renorm_image + delta
pca_color_image = pca_augmentation_version_renorm_image * std + mean
pca_color_image = np.maximum(np.minimum(pca_color_image, 255), 0).astype('uint8')