I would love to be able to use datasheets that are more flexible. As it is, if you want your datasheets to be even reasonably functional and friendly, you must do a lot of coding behind them. Even so, I do not know of a way to produce conditional formatting or to make any color changes at all. You can set the properties of the controls on the form, but when viewed in datasheet view, everything is black on white.
If you are familiar with and like using Visual Basic's datagrid controls, you will be disappointed with Access's measly offering.
I once saw a third party product which mimic's VB's datagrid but have forgotten where. I'll take a look around and post back here if I spot something promising.
Shep