I would suggest using the help entry for Conditional Formatting but I don't know how good the translation to Italian is so I posted two pictures. One shows the formatting dialog box (open form in design view, click on control to be formatted, select ConditionalFormatting from Format menu). I chose the expression option and entered an expression that would color all ID that are even, red. The odd values retain their default properties. The other picture shows the form in datasheet view so you can see the alternating colors.