Output all the white or black squares of a chessboard Introduction
This is how a chessboard looks like.

You can see that a1 is a dark square. However, b1 is a light square.
The Task
The challenge is, given dark, light or both, output all the dark, light or all squares with a separator (like a whitespace or a newline). The order of all the squares does not matter.
Test cases
Input: dark
Output: a1 a3 a5 a7 b2 b4 b6 b8 
        c1 c3 c5 c7 d2 d4 d6 d8 
        e1 e3 e5 e7 f2 f4 f6 f8 
        g1 g3 g5 g7 h2 h4 h6 h8

Input: light
Output: a2 a4 a6 a8 b1 b3 b5 b7 
        c2 c4 c6 c8 d1 d3 d5 d7 
        e2 e4 e6 e8 f1 f3 f5 f7 
        g2 g4 g6 g8 h1 h3 h5 h7

Input: both
Output: a1 a2 a3 a4 a5 a6 a7 a8
        b1 b2 b3 b4 b5 b6 b7 b8
        c1 c2 c3 c4 c5 c6 c7 c8
        d1 d2 d3 d4 d5 d6 d7 d8
        e1 e2 e3 e4 e5 e6 e7 e8
        f1 f2 f3 f4 f5 f6 f7 f8
        g1 g2 g3 g4 g5 g6 g7 g8
        h1 h2 h3 h4 h5 h6 h7 h8

Note: I have prettified the output but this is not necessary.
This is code-golf, so the submission with the least amount of bytes wins!
Pyth, 22 21 bytes
-1 byte by @Sp3000
fn%Chz3%sCMT2sM*&lt;G8S8

Under the function %Chz3, dark hashes to 1, light to 0, and both to 2. If we take the parity of the sum of the ords of a chess square (that is, a1 -&gt; [97, 33] -&gt; (97 + 33)%2 = 0, dark squares go to 0, and light to 1. This allows us to filter by inequality.
fn%Chz3%sCMT2sM*&lt;G8S8      implicit: z=input
               *           Cartesian product of
                &lt;G8          first 8 letters in G (alphabet)
                   S8        with [1,...,8] implicitly stringified
             sM*&lt;G8S8      ['a1','a2,...,'a8','b1'...'h8']
f          T               Filter that by gives truthy result to lambda T:
        sCMT                   The sum of the ords of the chars in T,
       %    2                  modulo 2
 n                            does not equal
   Chz                          ord of the first char in z,
  %   3                         modulo 3
                            Implicitly print the list.

Try it here.