When a command block has a command in it similar to "/say §a Mine Craft", only the word "Mine" would be colored, not the word "Craft". Before the introduction of the tellraw command, both words would be colored.
I do not think this is intentional, as all words after the color code are colored when you look inside the command block to set the command, but not when the command block outputs.
1. Enter "say §aHey Guys!" (May require some external editing)
2. Power command block
3. Only the word "Hey" will be colored
Attached are a screenshot of how it should look, and what it does look like currently.
(First bug report, hopefully I did that right! )