Oda has made the difference between "greatest" and "strongest"
If he wants to say greatest, he would use "ichi no" (like he did in chapter 700)
If he wants to say strongest, he would use "saikyou" (like he did in all other instances when describing Mihawk)
Its like calling Whitebeard (sekai...
Not sure what being coloured have to do with anything
I never denied Zoro saying he wants to be "strongest daikengo"
But he has also said he wants to be the "strongest kenshin"
And we know Shanks is a "kenshin"