My hair is yours..
dark
darker
dark than
darker than

Darker than

Explanation:

My hair is dark yours. (Incorrect. Grammar does not make sense. You don't use this when comparing one thing to another)

My hair is darker yours. (Incorrect. Grammar is incorrect)

My hair is dark than yours (Incorrect. You still don't use Dark when comparing)

My hair is Darker than yours (Correct! The grammar is correct and the correct comparative form)

When comparing one thing to another you add -er.

When you are comparing 3 or more things you add -est.

(Sherry is the greatest singer in the quoir)

(Yui has larger eyes than Terri)

faithful servants eumaeus and philaetius:

his ragged vest then drawn aside disclosed the sign conspicuous, and the scar exposed: eager they view'd, with joy they stood amazed with tearful eyes o'er all their master gazed:

these servants know ulysses by the scar he got when he was a child - so when he showed them the mark, they immediately knew this is truly their master and they hugged him, finally starting to believe his words.