The 'halo' around a horse's ears are normal... its the fold where on one side the hair grows out, and the other side the hair grows in. A lot of the photos you see of horses when they're totally dolled up, people have shaved the inside and trimmed the outside of the ear, eliminating the 'halo'. =)
ETA: Wanted to make it a bit more clear. Where the hair grows out, the light can get through it, versus the 'in' hair which is shrouded by the ear itself, giving the halo appearance. I'm not sure I'm making much sense, but I'm trying!