the thing is Access (and other databases) deal with set theory - your datasheet is a set (collection) of data satisfying certain criteria, and therefore there IS, per se, no logical distinction between the rows that Access can use intrinsically to affect the colouring
I presume MS realised this was a practical issue, and partially solved it by offering the 'limited' conditional formatting, but this applies to continuous forms only, rather than datasheets, I think. Conditional formatting has the appearance (to me) of being a bolt on addition, rather than a native feature.
the thing is, in a spreadsheet, the colouring isnt really an attribute of the data, its an attribute of the row or column - if you do this in a spreadsheet, the colouring is valid only for a certain order - if you reorder the xl sheet, the colours will become meaningless.
Now Access deals with columns fine - its all based on columns (fields), but it doesn't really understand rows (without user stipulation, the data is just presented in any arbitrary order).