Memory channel confusion?

ok, I can find plenty of references to memory for the compaq 6000 pro SFF but only the following illustration which is not what i see in this computer

http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/psi/mostViewedDisplay?javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken&javax.portlet.prp_efb5c0793523e51970c8fa22b053ce01=wsrp-navigationalState%3DdocId%253Demr_na-c02032590-1%257CdocLocale%253Den_US&javax.portlet.tpst=efb5c0793523e51970c8fa22b053ce01&sp4ts.oid=4023814&ac.admitted=1410398941045.876444892.199480143

currently the black is not populated, it has a 2gb ram module in the white slot above the black slot, if i out it in black it gives beep warning

also, it is other way around, black at the bottom away from the CPU.

all i want to do is replace ram with 2 X 2gb modules but it is not clear to me which slots to use.