Note, that the color-coding on your motherboard RAM slots is not just for 'kicks', the color pairing are the two channels (A and B) that your motherboard owners manual refers to. If you do mix and match ALWAYS do it in pairs.In your case, you will encounter decreased performance (even if you do get the extra memory mapped) because you will not benefit from a dual-channel configuration see: What is dual channel memory?.It's not a good idea to mix-and-match your RAM, different sizes and vendors.
There could be a few reasons why your memory isn't usable.
