umbrella tag for colored sclera

BUR #4329 has been approved by @evazion.

create implication black_sclera -> colored_sclera
create implication yellow_sclera -> colored_sclera
create implication red_sclera -> colored_sclera
create implication blue_sclera -> colored_sclera
create implication green_sclera -> colored_sclera
create implication purple_sclera -> colored_sclera
create implication pink_sclera -> colored_sclera
create implication orange_sclera -> colored_sclera
create implication grey_sclera -> colored_sclera
create implication brown_sclera -> colored_sclera
create implication aqua_sclera -> colored_sclera

It's really hard otherwise to search for colored scleras in general.
Now, to address the elephant in the room, black sclera has more posts than all the other versions combined. I don't feel like it makes sense to leave it out however, since it's still a different color than the normal white.

Somewhat related, but a thing to note is that human eyes are apparently unique from much of the animal kingdom. Apparently our sclera is particularly pale compared to the iris and our irises are relatively small compared to the eye, so for most animals you won't really see the sclera visible. Given this, we should probably avoid tagging animals using these tags. For example post #2376185 which is tagged "blue sclera", "brown sclera", and "aqua sclera." Given how most cat's eyes are, what we're tagging as sclera is most likely their iris instead.

The bulk update request #4329 (forum #178213) has been approved by @evazion.