V2010:
Open the form in datasheet view.
You should see a context Ribbon with main tab title "FORM TOOLS" sub heading "Datasheet"
Formatting subgroup.
You can set the background colour and the alternate row colour within this ribbon.
Setting these from the properties sheet appears to just effect the single/continuous form views.
Also via vba:
give the form a module
(just something with an event - even the onload just something)
Then using the intlisense:
me.datasheet____________
will give you a list of the datasheet background etc. You can select one of these and then [F1] for more information as some of these were added starting with V2007.
For the v2003:
DatasheetBackColor Property [Access 2003 VBA Language Reference] you can look at the others within the list to the left.
I'm sure there's something along the same lines for V2007/2010; however, I don't have time to hunt it down today.