Do I stick my sticks of RAM in the same colour or the same "channel"?

Ok this should be my final question based on my computer as this is the last thing that needs fixing.

I had to send my other chips of RAM back as one was defective and they wanted to have both as they came from a pack. I picked up a pair of Kingstone 1333MHz RAM for my Asus M4A77T Mobo.

Links for these two are below:
http://www.dabs.com/products/kingston-valueram-4gb--2x2gb--1333mhz-ddr3-non-ecc-cl9-dimm-240-pin-5KNM.html
http://www.cclonline.com/product-info.asp?product_id=47782&tid=gsearch

Basically the mobo comes with 4 slots for my RAM. These are in two colours: black and blue and are labeled A1, B1, A2, B2 where A1 and B1 are black and A2 and B2 are blue.

What I was questioning is whether I am supposed to put them in the same channel – so one in A1 and one in A2, or whether I put them in the same colour.

I read the booklet which came with the mobo and it only says for the best overclocking for RAM over 1600MHz is to put them in both the blue slots. So I instinctively put them in the black slots since my RAM is only 1333MHz.

Some other questions: what does it mean by the same channel? What differences are there having them in different channels (say A1 and B1)?

At the moment they are in A1 and B1 – the black ones, and the computer turns on. But I wanted to know if I get more out of the RAM by sticking them in A1 and A2. Or does it ultimately not make any difference?