Sign colors

When I play on my MacBook Pro Sign Colors on servers do not work

What I expected to happen was...: See Colors on signs (in servers)
Describe what you thought should happen here: see server colors.

What actually happened was...: I Did Not se colors on signs, only blacck font
Describe what happened here: When I Play Minecraft multiplayer pc version, I Do Not see colors on signs unless i look from a certain angle. I will Attach a picture of what kind of mac i have.

Steps to Reproduce:
STEPS: N/A
Here is a video of a mod to fix the problem: http://www.youtube.com/watch?v=P8GOAH_2Ko8