Most likely because when you got their genes, their 'color blind' gene came out recessive from BOTH parents. Recessive just means that the gene isn't expressed, but you still have it in your DNA.
If both my parents are color blind then why am I not color blind?
Yes, David is right. But there's one more thing you should know. Are you a girl child?
In many cases, the daughters are carrier of the gene/s. So, the symptoms do not show in them.