2 RAM slots not working properly

[minecaust]

I am using a ASUS M5A99FX PRO R2.0 motherboard along with 2 x 8GB G.Skill Ares ddr3.

I have always used the black ram slots until recently when my computer started giving me an error saying "Your computer is running low on memory" nearly every time I played a game.

http://imgur.com/XhD1WTB

I switched them to the blue slots and now everything seems to work perfect. No more error messages.

My questions are:

1. Why did it start doing this?
2. Is there a way to fix it?
3. Is there a deeper underlying problem?
4. Is there a decrease in performance by using the blue slots instead of the black ones?

Thank you to anyone willing to help me with my problem!

Memory I use: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231546

Motherboard I use: http://www.newegg.com/Product/Product.aspx?Item=9SIA1N83UD9887

 

[Tradesman1]

What CPU? Were you running the DRAM at 1600 or...??? What is DRAM running at now???

 

[gskill support]

Blue slots is perfectly fine. They are the slots you should be using.