honestly i think it's lighting (and dilation) that creates the red eye effect. i've seen pix of the same BEL's that have the red pupil in some pix and the same BEL w/ black pupils in other pix. RedSheperd's (on the forum here) own BEL comes to mind.
Honestly, that was my initial thought. However, my BELs eyes are always red. Low light, artificial light, natural light.