My stallion has completely dark scleras unless he really opens his eyes wide.
My gelding shows a little bit of white even when relaxed...the sclera is just
a tiny bit mottled. My friend's mare has probably 25% dark/75%white sclera
showing normally. A filly I looked at had one eye with dark sclera and one
with mostly white. All these are purebred Arabs. None had extensive facial
markings. Maybe you are seeing mismatched eyeball coloration, instead of one
eye being opened wider or looking in a funny direction.
Shelly