expression, ichidan verb
add a little extra; sweeten the deal; shade an account
Idiomatic expression meaning to add a small bonus, discount, or favorable adjustment, often in business or financial contexts. The literal meaning is 'to add color'.
値段に色を付けてくれた。
They gave me a little extra discount.
帳簿に色を付けるのはよくない。
It's not good to shade the accounts.