Question: How do I show that picking 3 socks containing just black and red socks that I must get either a pair of black or red socks?

I mean it's fairly obvious, but how would I show it?

Is this pigeon hole?

Answer: 
Two holes: red and black........
We can use the Pigeonhole Principle (strong form). That is $q\_1+q\_2+⋯+q\_n−n+1$ where $q\_i$ is the number of desired socks of a certain color, $(2)$ and $n$ is the number of colors, $(2)$. So $2+2-2+1=3$.