Another explanation:
Hola 1 and Hola 2 are both holas. Holas can be only blue or red. Each hola has a 1/2 chance of being blue and a 1/2 chance of being red.
The EQUALLY LIKELY possibilities are:
* both red (1/4)
* Hola 1 is red, Hola 2 is blue (1/4)
* Hola 1 is blue, Hola 2 is red (1/4)
* both blue (1/4)
Now if we say: "One of the holas is red", it doesn't specify Hola 1 as red, or Hola 2 is red- just either of them. Thus the only thing that rules out is the last option (both blue)
we are left with:
* both red (1/4)
* Hola 1 is red, Hola 2 is blue (1/4)
* Hola 1 is blue, Hola 2 is red (1/4)
but they're 1/3 now, not 1/4, because they are all equally likely (1/4) but one of the chances has been axed out, leaving them all equally likely out of 3