or try to think of a new letter to the alphabet
there were 428 letters in that one episode of spongebob in the future
We can see every color in the visible spectrum. Colors aren't like animals. Dr.Seuss could imagine new animals all day, but there is a finite number of colors, and we can already see all of them. There simply aren't anymore to imagine.
Not really. In actuallity there are colors invisible to us such as a certain "red-green". Googke it :)